Drug and Alcohol Services Council South Australia

Respiratory harms of smoked cannabis

Linda R. Gowing1, Robert L. Ali1, 2 and Jason M. White1,2

DASC Monograph No 8

Research Series

1Drug and Alcohol Services Council, South Australia 2Department of Clinical and Experimental Pharmacology, University of Adelaide

July 2000

© Drug and Alcohol Services Council 2000 Drug and Alcohol Services Council 161 Greenhill Road Parkside SA 5063 Australia ISBN 0-7308-6227-5

i

T A B L E O F C O N T E N T S LIST OF TABLES AND FIGURES .......................................................................................... ii

ACKNOWLEDGMENTS ........................................................................................................ iii

EXECUTIVE SUMMARY ...................................................................................................... iv

SECTION 1 INTRODUCTION ...........................................................................................1

Prevalence of cannabis use...........................................................................1

Evidence of respiratory risk ...........................................................................1

Smoke and smoking behaviour ......................................................................2

Aims of this study .........................................................................................2

SECTION 2 METHODS....................................................................................................4

Samples .......................................................................................................4

Sample preparation ......................................................................................4

Smoking procedure.......................................................................................4

Definitions and methods of chemical analysis ................................................5

Data analysis ...............................................................................................5

SECTION 3 RESULTS .....................................................................................................6

Cannabis samples ........................................................................................6

Relationship between water in smoke and yield of THC ..................................8

Tar and carbon monoxide content of cannabis smoke...................................10

Comparison of cigarettes and water pipes ...................................................11

Effect of adding tobacco .............................................................................14

SECTION 4 DISCUSSION .............................................................................................16

THC content of cannabis and cannabis smoke .............................................16

Tar levels ...................................................................................................18

Carbon monoxide........................................................................................20

SECTION 5 CONCLUSIONS AND RECOMMENDATIONS ...............................................22

REFERENCES ........................................................................................................24

ii

L I S T O F T A B L E S A N D F I G U R E S

Table 1 Nature of sample, THC content of plant material and smoke ...........................6

Table 2 Water content of smoke and yield of THC ......................................................8

Table 3 Tar and carbon monoxide content of smoke from 100% cannabis

cigarettes ...................................................................................................10

Table 4 Total tar and carbon monoxide content – shorter puff interval and

cigarettes versus water pipes ......................................................................11

Table 5 Effect of tobacco on THC, tar and carbon monoxide content of smoke...........15

Figure 1 Relationship between THC content of plant material and THC

content of smoke ..........................................................................................7

Figure 2 Relationship between water in smoke and yield of THC ..................................9

Figure 3 Tar in smoke from cannabis cigarettes and water pipes ................................12

Figure 4 Carbon monoxide in smoke from cannabis cigarettes and water pipes ...........13

iii

A C K N O W L E D G M E N T S

The data reported in this paper is derived from work undertaken by the Australian Government

Analytical Laboratories, Melbourne, on behalf of the Commonwealth Department of Health and

Aged Care. The authors acknowledge the assistance of the Commonwealth Department of

Health and Aged Care in releasing the data on which this paper is based, Karen Hutchinson for

her work to assess the data, Wayne Hall and Donald Tashkin for initial discussions on the

study.

iv

E X E C U T I V E S U M M A R Y

This study aimed to consider the source of respiratory risks from cannabis smoking using

analyses of the major components of cannabis smoke in conjunction with literature evidence.

Levels of major analytes in smoke from cannabis and cannabis/tobacco mixtures smoked as

unfiltered cigarettes or via water pipes were compared. The cannabis samples analysed were

police seizures, provided by Federal and State police.

Data from this study shows that cannabis being sold on the streets varies widely in

tetrahydrocannabinol (THC) content.

While there was a significant correlation between the THC content of the plant material and the

THC content of smoke from cannabis water pipes, this was not the case for smoke from

cannabis cigarettes. At the same time, for both cannabis cigarettes and water pipes there was

a correlation between yield of THC (ie. the proportion of THC in the original plant material

released into the smoke) and the amount of water in the smoke. These findings are suggestive

of variability in the burning properties of the cannabis samples. It is possible that some

samples burn more readily, thereby achieving a higher burning temperature and resulting in

the release of greater amounts of water and THC. The burning temperature was not measured

in this study, preventing exploration of this hypothesis.

The tar content of smoke from pure cannabis cigarettes was, in most instances, lower than that

of reference (unfiltered) tobacco cigarettes, but would be higher than that of commercially

manufactured filtered tobacco cigarettes. The carbon monoxide yield of cannabis cigarettes

was in a similar range to that of the reference tobacco cigarettes.

Comparison of smoke from cannabis cigarettes and water pipes was limited by the need to

reduce the inter-puff interval for water pipes in order to keep the cannabis sample alight in the

water pipe cone. Levels of both tar and carbon monoxide are higher in smoke from cannabis

water pipes compared to cannabis cigarettes. The different smoking conditions account for

some, but not all, of the increase. The remaining difference may be attributable to the filtering

v

effect of the cigarette butt. If cannabis smokers do not leave a butt, or incorporate the butt end

into a new cigarette, the difference between cigarettes and water pipes, in terms of tar and

yield, may well disappear.

This study looked only at THC and total particulate matter. It is possible that water filtration

may have a differential effect on THC and other cannabinoids relative to each other, or relative

to overall tars. It is also possible that water filtration may differentially affect levels of

carcinogenic components of “tar”. This would be a useful area of future investigation.

When tobacco was added to cannabis, tar levels in smoke from cigarettes, but not water pipes,

increased. This suggests that the different smoking conditions used for the water pipes may be

the major factor influencing the release of tar. The addition of tobacco increased carbon

monoxide in smoke from both cigarettes and water pipes.

Overall, this study suggests that the respiratory risks of cannabis smoking may be able to be

reduced to some extent if cannabis is smoked as a cigarette, rather than via a water pipe,

without the addition of tobacco. Smoking without deep inhalation or breath-holding may also

help to reduce harms as studies reported in the literature suggest that these practices may

increase respiratory risks, by increasing absorption of carbon monoxide and deposition of tars,

with little change in cannabinoid effects.

Future research should address:

• the effect of smoking conditions, smoking mechanism and the addition of tobacco on yield

of tar and carbon monoxide relative to THC and other cannabinoids;

• the effect of burning temperature on the release of cannabinoids, tars and carbon

monoxide;

• the effect of water filtration on levels of THC and other cannabinoids, relative to tars, and

levels of carcinogenic components of tar.

Such information is relevant to future therapeutic applications of cannabis using inhalation as

route of administration, as well as to measures to address the public health impact of

cannabis use.

1

S E C T I O N 1 I N T R O D U C T I O N Prevalence of cannabis use1

Surveys in the USA, Canada, Australia, Europe and the United Kingdom have produced similar

findings in showing that approximately one third of the adult population report cannabis use at

some point in their life. Estimates of the prevalence of regular cannabis use are much lower.

The proportion of the adult population to have used cannabis recently (in the year prior to

survey) has been estimated at 9% for the USA in 1992, 7.4% for Canada in 1994 (WHO Expert

Working Group on Health Effects of Cannabis Use, 1997) and 13% for Australia in 1995. As a

comparison, the same Australian survey found that 26% of the adult population were current,

regular or occasional smokers of tobacco (National Drug Strategy Household Survey, Survey

Report 1995). The 1998 National Drug Strategy Household Survey found 17.9% of the adult

population had used cannabis in the year prior to the survey, compared to 26.3% who had

used tobacco (Australian Institute of Health & Welfare, 1999).

In the context of high prevalence of cannabis use, adverse health consequences arising from

use are a potentially significant public health issue. In broad terms, the health consequences

of cannabis use comprise the psychoactive effects of cannabis and the respiratory risks of

smoking as a route of administration (WHO Expert Working Group on Health Effects of

Cannabis Use, 1997). Only the respiratory risks of cannabis smoking are considered in this

paper.

Evidence of respiratory risk

Cannabis is most commonly used by smoking (Makkai & McAllister, 1997) and, on the basis of

qualitative similarities in the composition of smoke from tobacco and cannabis, it has been

assumed likely that long-term habitual use of the two drugs is associated with many of the

same health consequences (Van Hoozen & Cross, 1997). Indeed, the chronic smoking of

cannabis has been linked to increased risk of respiratory disease, and oral and lung cancers

(Hall et al, 1994; WHO Expert Working Group on Health Effects of Cannabis Use, 1997).

Heavy cannabis smokers and heavy tobacco smokers both report more adverse respiratory

symptoms than non-smokers, although cannabis smokers report fewer symptoms than tobacco

1 In this paper the term “cannabis” is used in a generic sense, covering the variety of preparations derived from the plant Cannabis sativa including marijuana, hash and hash oil.

2

smokers (Zimmer & Morgan, 1997). Common side effects noted by users include cough,

dyspnoea, sore throat, nasal congestion, and bronchitis (Van Hoozen & Cross, 1997).

Furthermore, regular smoking of marijuana has been found to be associated with airway

inflammation and cellular alterations of a type and degree similar to those found with tobacco

smoking (Barsky et al, 1998; Roth et al, 1998).

Smoke and smoking behaviour

Respiratory risks can be influenced both by the substance being smoked and by smoking

technique. Factors influencing risk that are common to both tobacco and cannabis include the

tar and carbon monoxide (CO) content of smoke, frequency of smoking, and smoking

behaviour, which can be characterised in terms of the interval between puffs, depth of

inhalation and breath-holding. There are a number of behaviours specific to cannabis that

might also influence the respiratory risks of cannabis smoking. Cannabis is generally smoked

as unfiltered handmade cigarettes or through a water pipe and it is common for users to blend

cannabis with tobacco to use expensive cannabis supplies economically and improve burning

properties.

The reasons for the preferences of smokers are not always clear. When comparing cigarettes

and water pipes the sensory qualities of the smoke may be important. Preferences for water

pipes may also be driven by the easier handling and reduced wastage of flowering heads. The

heads are generally smoked in small amounts because of their higher content of the major

psychoactive compound, tetrahydrocannabinol (THC) and higher price. A further factor is the

belief, held by some users, that the smoke from water pipes is safer due to the cooling and

filtering effect of the water.

Aims of this study

Analyses of smoke from a variety of tobacco products have been undertaken routinely for

many years. This study represents the first time that similar analyses have been undertaken

for a number of cannabis samples. As the samples used were all police seizures they are

representative of products that are being made available to cannabis users.

3

This paper examines the results of analyses of tar, carbon monoxide and THC content of

smoke from cannabis and cannabis/tobacco blends to consider the factors contributing to the

risks of respiratory harm from cannabis smoking.

This analysis is significant from a public health point of view in terms of indicating mechanisms

to reduce the harms of cannabis use. It is also of relevance to potential therapeutic application

of cannabis for which inhalation may be a more effective route of administration (Gowing et al,

1998).

4

S E C T I O N 2 M E T H O D S

Samples

The Federal and various Australian state police forces were approached to provide cannabis

samples seized in their areas. In order to provide a range of THC values, each jurisdiction was

asked to provide two separate seizures, one of predominantly leaf material, the other of

predominantly flowering heads. A total of 12 cannabis samples were received. White Ox loose

cigarette tobacco was purchased for blending.

Sample preparation

Two hydroponically grown cannabis samples (samples 11 and 12) arrived as fresh green

material. They were dried at 40°C before conditioning. All samples were conditioned in a

controlled environment room at 22°C and 60% relative humidity. The samples were groomed to

remove stalks and twigs and homogenised in a low speed blender/shredder. Cannabis/tobacco

blends were prepared by first hand mixing the appropriate weights of each material and then

homogenising the mix in a low speed blender/shredder.

Cigarettes were rolled to a length of 70mm using hand held rolling machines commonly

available at tobacconists (Etai Express). Each cigarette was weighed before analysis and

contained an average 0.9g of material.

Smoking procedure

The samples were smoked on a Filtrona SM400 20 port linear smoking machine. Particulate

matter was trapped in Cambridge type four filter holders loaded with 44mm glass fibre filters.

The smoking machine was adapted to accommodate a two-chamber water pipe. The smaller

(approximately 70mL) first chamber was attached to a 250mL Dreschel bottle and head. The

first chamber was filled with 30mL and the second with 180mL of water.

Cigarettes were tested with three per port of the smoking machine and 25 ports per sample,

giving 75 cigarettes per sample. Water pipes were tested with two cones per port and up to 40

ports per sample, giving up to 80 cones per sample.

5

The cigarettes were tested following International Standards Organisation (ISO) methods for

the analysis of tobacco products, ie. 35mL puff volume, two second puff duration, 60 second

interval between puffs and 23mm butt length. Under these standard conditions it was found

that the samples in the burning cone of the water pipe would not stay alight between puffs.

Consequently, the water pipes were tested under the same puff volume and puff duration, but

at a six second puff interval. One blend of 50% cannabis/tobacco cigarette was also smoked

under these modified conditions for comparison purposes.

Definitions and methods of chemical analysis

Corrected particulate matter (referred to in this paper as “tar”) is, by ISO smoking definitions

for tobacco products, the weight of matter trapped by the standard filters corrected for water

and nicotine levels. Tar thus represents the amount of particulate matter to which the body is

exposed in order to gain access to nicotine, but not including nicotine or water.

In this study, achieving consistency with ISO smoking definitions for products containing

tobacco and cannabis would have required correction of the weight of matter trapped by the

filters for the primary psychoactive component (THC) as well as nicotine. However, there was

considerable variability in the THC assay of the trapped particulate matter that we are unable

to explain. Adjusting the total particulate matter for THC resulted in this variability also being

transferred to the calculated corrected particulate matter. To avoid this, for the purposes of

this study we have corrected the weight of matter trapped by the filters for water and nicotine,

but not THC. In this study, “tar” therefore represents the amount of particulate matter in the

smoke, including THC but not nicotine or water.

Nicotine and THC were determined on an HP 5890 Series II Gas Chromatograph (GC). The GC

analysis was done using 0.53mm diameter capillary columns. The initial THC levels in the

cannabis plant materials were determined by soxhlet extraction with hexane and GC analysis.

Data analysis

Smoke constituents are presented as milligram of analyte per gram of original plant material,

or as milligram of analyte per gram of material smoked (estimated from the weight of residual,

unburnt material). This overcomes the variable weight of material in individual cigarettes or the

cone of the water pipe.

6

S E C T I O N 3 R E S U L T S Cannabis samples

There was a 20-fold variation across the 12 cannabis samples in the THC content of the plant

material and in THC content of smoke from cigarettes and water pipes containing only

cannabis (Table 1).

Table 1: Nature of sample, THC content of plant material and smoke All data is for samples of pure cannabis. For cigarettes, each value is the mean from 25 ports of the smoking machine, three cigarettes per port. For water pipes, each value is the mean from between 15 and 40 ports, two cones per port.

Sample Nature THC (mg/g

plant material) THC in smoke (mg/g material

burnt)

Cigarette Water pipe

1 (Unknown) 5.7 3.8 1.4

2 Leaf 6.9 6.2 2.3

3 (Unknown) 8.1 4.8 2.0

4 Leaf 16.1 3.3 4.8

5 (Unknown) 17.5 4.1 0.8

6 (Unknown) 17.5 9.2 3.3

7 (Unknown) 18.4 1.7 11.4

8 (Unknown) 20.7 2.7 9.9

9 Heads 25.3 4.7 4.3

10 Heads 52.8 38.5 23.3

11 Hydroponic leaf 90.8 5.8 19.7

12 Hydroponic heads 129.7 5.4 23.9

There was a significant correlation between the THC content of the plant material and the THC

content of the smoke from water pipes (R=0.859, P<0.001) but not for smoke from cigarettes

(R=0.185, P=0.566). The lack of correlation is shown clearly by figure 1.

Figure 1: Relationship between THC content of plant material and THC content of smoke

0

5

10

15

20

25

30

35

40

45

0 20 40 60 80 100 120 140

THC in plant material (mg/g)

THC

in s

mok

e (m

g/g

smok

ed)

CigarettesWater pipes

8

Relationship between water in smoke and yield of THC

One of the variables calculated was that of yield, ie. the proportion of THC in the original plant

material that was released into the smoke. As a percentage of total THC, the yield in smoke

ranged from 4% to 89%. The cannabis samples used in this study were conditioned in a

controlled environment room prior to use so that the water content of the plant material should

have been the same. Despite this, there was considerable variation in the amount of water in

the smoke from cigarettes and water pipes containing only cannabis (Table 2).

Table 2: Water content of smoke and yield of THC All data is for samples of pure cannabis. For cigarettes, each value is the mean of results from 25 ports of the smoking machine, three cigarettes per port. For water pipes, each value is the mean from between 15 and 40 ports, two cones per port.

Sample Yield of THC in smoke relative to plant material (%)

Water in smoke (mg/g material burnt)

Cigarettes Water pipe Cigarettes Water pipe

1 66.4 25.3 4.9 179.3

2 89.1 33.9 5.3 157.0

3 59.5 24.1 5.5 147.4

4 20.5 29.7 4.7 112.4

5 23.2 4.7 4.7 55.9

6 52.8 19.0 4.7 96.2

7 8.9 61.7 1.3 135.1

8 13.1 47.6 2.6 137.6

9 18.7 17.0 4.0 92.1

10 72.8 44.1 6.7 196.6

11 6.4 21.7 0.9 67.8

12 4.1 18.4 0.7 67.1

Furthermore, there was a significant and positive correlation between the yield of THC in the

smoke and water content of the smoke from both cannabis cigarettes and water pipes

(R=0.616, P=0.033 for water pipes; R=0.810, P=0.001 for cigarettes). The data is presented in

Figure 2. The water in the pipe resulted in a high background level of water vapour in the

smoke, requiring a separate y-axis scale for the water pipe data but the pattern is similar for

both water pipes and cigarettes

Figure 2: Relationship between water in smoke and yield of THC

0

1

2

3

4

5

6

7

8

0 20 40 60 80 100

Yield of THC in smoke (%)

Wat

er in

sm

oke

from

join

ts (m

g/g

smok

ed)

0

50

100

150

200

250

Wat

er in

sm

oke

from

bon

gs (m

g/g

smok

ed)

CigarettesW ater-pipes

10

Tar and carbon monoxide content of cannabis smoke

White Ox tobacco was used for blending with cannabis and as a comparison for both joints and

bongs. In terms of the tar content of smoke, White Ox tobacco is about average for “roll your

own” tobacco. The data in table 3 shows that the tar content of smoke from pure cannabis

cigarettes is, in most instances, lower than that of the reference tobacco cigarettes. Carbon

monoxide levels are in a similar range.

Table 3: Tar and carbon monoxide content of smoke from 100% cannabis cigarettes Each value is the mean of results from 25 ports of the smoking machine, three cigarettes per port, for cigarettes containing cannabis only.

Sample Tar in smoke (mg/g material burnt)

Carbon monoxide in smoke (mg/g material burnt)

1 30.1 20.7

2 29.8 21.6

3 32.0 19.9

4 45.1 28.1

5 40.1 17.4

6 25.2 13.0

7 19.3 26.0

8 30.2 31.9

9 36.0 19.5

10 10.4 19.0

11 19.5 23.6

12 13.1 22.6

White Ox tobacco 44.2 26.9

11

Comparison of cigarettes and water pipes

Water pipes were smoked with a much shorter pause between puffs. This was because the

cannabis samples in the water pipe cones would not stay alight under the conditions used for

cigarettes. The smoke from cannabis water pipes contained much higher levels of tar and

carbon monoxide (Figures 3 and 4) but at least some of this difference is likely to be due to the

differing smoking conditions. Figures 3 and 4 also demonstrate that the tar and carbon

monoxide content of smoke is not correlated with the THC content of the plant material. Thus

smoking cannabis with higher THC content does not necessarily mean inhalation of more tar

and carbon monoxide – it is the smoking conditions that determine the tar and carbon

monoxide content of the smoke.

To gauge the effect of smoking conditions, one sample of cannabis (sample 2), mixed with

50% tobacco, was smoked as a joint with both 6 seconds and 60 seconds between puffs,

reflecting the smoking conditions used for the main testing of water pipes and cigarettes,

respectively. Comparing these results for the same sample smoked as a water pipe enables

some consideration of the extent to which differences are simply due to smoking conditions, as

opposed to the use of a water pipe (Table 4).

Table 4: Total tar and carbon monoxide content – shorter puff interval and cigarettes versus

water pipes Each value is the mean of results from the number of ports indicated. Cigarettes were smoked three to a port. Water pipes were smoked with two cones per port.

Puff interval Number of ports used

Tar in smoke (mg/g material

burnt)

Carbon monoxide in smoke (mg/g material burnt)

60s (cigarette) 25 50.6 30.1

6s (cigarette) 18 103.6 43.6

6s (water pipe) 41 153.3 122.4

This data indicates that, for this sample, approximately two-thirds of the increase in the tar

content and one-third of the increase in carbon monoxide content of cannabis smoke can be

attributed to the reduction in puff interval.

Figure 3: Tar in smoke from cannabis cigarettes and water pipes

020406080

100120140160180200

0 20 40 60 80 100 120 140

THC in plant material (mg/g)

Tota

l tar

in s

mok

e (m

g/g

burn

t)

CigarettesWater-pipes

Figure 4: Carbon monoxide in smoke from cannabis cigarettes and water pipes

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140

THC in plant material (mg/g)

CO

in s

mok

e (m

g/g

burn

t)

CigarettesWater-pipes

14

Effect of adding tobacco

All samples were smoked as 100% cannabis, and as a 50% mixture with tobacco, in both

cigarettes and water pipes. Table 5 shows levels of THC, tar and carbon monoxide (as mg/g of

material smoked) in smoke from cigarettes and water pipes containing pure cannabis or a mix

of 50% cannabis and 50% tobacco. (For cigarettes, each value is the mean from 25 ports of

the smoking machine, three cigarettes per port. For water pipes, each value is the mean from

between 15 and 40 ports, two cones per port.) The percent change was calculated as:

(50% value – 100% value) x 100. 100% value

By and large, with water pipes, the addition of 50% tobacco reduced the THC levels by around

half, but with cigarettes it is a different matter. In three samples (7, 11, 12) THC levels actually

increased following the addition of tobacco (Table 5).

Turning to the effect of adding tobacco on the tar content of the smoke, the data in table 5

shows that, for most samples smoked as cigarettes, tar levels increase. The effect on tar

levels in smoke from water pipes is minimal.

Finally, looking at carbon monoxide, the addition of tobacco increased carbon monoxide for all

samples. The increase appears to be more marked with water pipes but the difference between

water pipes and cigarettes was not statistically significant.

Table 5: Effect of tobacco on THC, tar and carbon monoxide content of smoke

Cigarettes THC TAR CO Sample 100%

cannabis 50% cannabis

% change 100% cannabis

50% cannabis

% change 100% cannabis

50% cannabis

% change

1 3.8 0.5 -87 33.9 37.1 9 20.7 26.3 27 2 6.1 0.9 -85 36.0 50.6 41 21.6 30.1 39 3 4.8 0.6 -88 36.8 46.4 26 19.9 26.8 35 4 3.3 1.5 -55 48.4 52.3 8 28.1 35.2 25 5 4.1 0.3 -93 44.1 53.0 20 17.4 32.6 15 6 9.2 1.9 -79 34.6 61.4 77 13.0 31.6 143 7 1.6 1.8 13 20.9 38.9 86 26.0 32.1 23 8 2.7 1.9 -30 32.9 44.5 35 31.9 35.6 12 9 4.7 2.2 -53 40.7 43.1 6 19.5 28.7 47 10 38.5 5.4 -86 48.9 56.5 15 19.0 28.6 51 11 5.8 6.9 19 25.4 44.1 74 23.6 30.5 29 12 5.4 9.8 81 18.4 47.1 156 22.6 30.6 35 Water pipes THC TAR CO

Sample 100% cannabis

50% cannabis

% change 100% cannabis

50% cannabis

% change 100% cannabis

50% cannabis

% change

1 1.4 0.8 -43 133.5 138.4 4 79.1 149.9 90 2 2.3 1.6 -30 157.0 153.3 -2 84.9 153.2 80 3 2.0 1.1 -45 169.0 137.6 -19 89.6 139.1 55 4 4.8 3.0 -38 148.9 138.9 -10 73.4 149.4 104 5 0.8 0.5 -38 132.2 128.6 -3 56.4 61.5 9 6 3.3 2.3 -30 120.0 163.0 36 57.2 116.8 104 7 11.4 5.1 -55 151.7 163.7 8 98.5 138.2 40 8 9.8 5.0 -50 175.3 144.0 -18 113.6 121.5 7 9 4.3 4.0 -7 159.9 155.9 -4 62.0 129.8 109 10 23.3 10.6 -55 186.9 174.5 -7 107.7 121.8 13 11 19.7 11.2 -43 167.1 183.2 10 68.5 124.8 82 12 23.9 17.7 -26 141.9 134.3 -5 70.8 142.5 101

16

S E C T I O N 4 D I S C U S S I O N

The data reported here show that tar and carbon monoxide content of smoke is increased

when tobacco is blended with cannabis, when puff frequency is increased or when smoking is

via a water pipe rather than an unfiltered cigarette.

These findings parallel those obtained from studies of the tar yield of tobacco. Different brands

of cigarette and tobacco vary considerably in the tar content of the smoke they produce, and

tar levels are increased up to ninefold when the small ventilation holes in the filters of low tar

cigarettes are blocked (Winstanley et al, 1995).

The data also show that smoking cannabis with a high THC content will not ensure the

production of smoke that is also high in THC. The finding of a significant, positive correlation

between THC yield and water content of the smoke from pure cannabis indicates that other

factors are important in determining the release of THC.

These data should be interpreted with some caution since people do not smoke in the same

way as a machine. The levels obtained by mechanical means may not, therefore, represent the

levels ingested by the smoker. This study used a smoking machine modified to simulate one

type of water pipe but there is considerable variation in water pipes used by cannabis

smokers, ranging from those created from plastic drink bottles, to elaborate hookahs. It is not

known to what extent water pipe design may influence tar levels, or the extent of cooling of the

smoke. Despite these limitations, the data from smoking machine analyses nonetheless

provide an indication of factors influencing relative smoke composition, and hence relative

respiratory risks.

THC content of cannabis and cannabis smoke

This study found a 20-fold variation in the THC content of cannabis samples seized by police.

Those samples known to be grown hydroponically and those known to be comprised

predominantly of flowering heads contained the highest levels of THC, but the nature of a

number of samples is uncertain.

17

The THC content of cannabis is known to vary widely depending upon the variety and the

growing conditions (WHO Expert Working Group on Health Effects of Cannabis Use, 1997).

The flowering tops and bracts are highest in THC concentration, with potency descending

through the upper leaves, lower leaves, stems and seeds (Hall et al, 1994). The proportions of

these different parts of the plant in the material smoked will therefore influence the THC

content. A large number of samples would need to be analysed to explore the relative

contributions of these various factors to determining the THC content of cannabis.

It would seem logical that the THC content of smoke would reflect the THC content of the plant

material. The results of this study suggest that the THC content of the original plant material is

only one factor contributing to the amount of THC inhaled.

As THC is not water soluble, the correlation between yield of THC in the smoke and water

content of the smoke suggests that there is a factor influencing both THC and water release.

One possibility is the burning properties of the cannabis samples. A sample that burns more

readily would be expected to achieve a higher temperature, thereby possibly vaporising more

water and THC.

Diluting cannabis with 50% tobacco would, logically, lead to THC levels in the smoke reducing

by about half. The increased THC levels seen with three samples smoked as cigarettes was,

therefore, somewhat unexpected (Table 5).

Three samples all had low yield of THC when smoked as pure cannabis cigarettes (8.9%, 6.4%

and 4.1%, respectively). We suspect these samples were not burning well as pure cannabis,

that the burning temperature was increased by the addition of tobacco (which contains additive

to improve burning properties), thereby increasing the release of THC. The yield also

increased when these samples were smoked as pure cannabis in a water pipe, with the shorter

puff interval probably also increasing the burning temperature. However, as burning

temperature was not measured, this remains speculation on our part. Overall, the addition of

tobacco probably does reduce THC levels in smoke, as would be expected.

18

Further exploration of the factors influencing the release of THC into smoke will be important

to the development of mechanisms for reducing the respiratory risks of cannabis smoking by

increasing the availability of THC relative to tar and carbon monoxide.

Tar levels

Tar levels are relevant to respiratory risk in two regards. Firstly, interference with the body’s

methods of filtering inhaled air can contribute to the development of chronic obstructive

pulmonary diseases including bronchitis and emphysema. Secondly, the presence of

carcinogens increases the risk of cancers of the respiratory tract (Winstanley et al, 1995).

There is some evidence, albeit on small case numbers, of an association between long-term,

habitual cannabis smoking and the development of respiratory tract cancers in adults less than

40 years of age (Van Hoozen & Cross, 1997; WHO expert working group on health effects of

cannabis use, 1997). At present, the mutagenicity of individual constituents has not been

systematically evaluated (Van Hoozen & Cross, 1997) but they are likely to differ in their

carcinogenic properties. Zimmer & Morgan (1997) cite two studies comparing benzopyrene (a

carcinogen) content of cannabis and tobacco, one of which found a higher and one a lower

level. The WHO expert working group (WHO Expert Working Group on Health Effects of

Cannabis Use, 1997) cites a further study that found smoke from cannabis to have 50% more

carcinogens than the comparable quantity of unfiltered tobacco.

The apparent variability in burning properties of the cannabis samples used in this study, and

the variability of the assay for THC in smoke limit the extent of analysis of this set of data. In

particular, it was not possible to consider levels of tar relative to THC in the smoke. It also was

not possible to use statistical methods to test for significant changes in smoke content under

the various conditions used. However, the data indicates that total tar levels may be increased,

to varying extents, by a reduction in puff interval, by smoking via a water pipe rather than an

unfiltered cigarette (Table 4), and by the addition of tobacco to cannabis (Table 5). The

addition of tobacco to cannabis, in most cases, resulted in increased tar content when samples

were smoked as cigarettes, but had a minimal effect on tar levels for samples smoked in water

pipes. This suggests that the shorter puff interval used for the water pipes may be the major

factor influencing the release of tar.

19

In the study reported here, one brand of loose tobacco was used to blend with the cannabis

samples. This particular brand of tobacco is known to be similar to other loose tobaccos in

terms of tar and carbon monoxide levels of smoke but, while some users may mix their

cannabis with loose tobacco, others use tobacco extracted from commercial filtered cigarettes.

Loose tobacco may differ from commercial filtered cigarettes in tar yield and additives

(Winstanley et al, 1995) which might influence the burning properties of cannabis. However,

previous research using loose tobacco has shown that it is the selection of paper and filter that

has the greatest effect on tar and CO levels (Kaiserman & Rickert, 1992).

Research undertaken in the 1960s using tobacco indicated that water filtration reduces the

amount of particulate matter and carcinogenic potential of smoke (Cozzi, 1993). The data

reported here is not consistent with water filtration reducing total particulate matter but it is an

important point that only the total particulate matter was assessed with no distinction between

the individual components of “tar” or the effect on carcinogenic potential. When further data is

available on the mutagenicity of individual components of cannabis smoke it will be important

to examine the effect of water pipes, the use of a filter and the blending of cannabis and

tobacco on the release into smoke of these particular components.

The higher tar content of cannabis smoke from a water pipe compared to that from a cannabis

cigarette may reflect the filtering action of the cigarette butt. For this study, a butt length of

23mm was retained for cigarettes, but a butt does not exist for water pipes. Tashkin et al

(1991b) found that more complete smoking of the proximal end of the cannabis cigarette

delivers more tar, carbon monoxide and THC to the lungs. Furthermore, Gieringer (1996)

reports that a cigarette filter retains 30% more tar than does an unfiltered cigarette.

The cannabis cigarettes were smoked under standard conditions for analysis of tobacco

cigarettes, which means a butt of 23mm was left. If cannabis smokers are leaving a much

smaller butt, or if they are incorporating the butt end into a new cigarette it is possible that the

difference between cigarettes and water pipes, in terms of the tar content of smoke, may

disappear.

A study sponsored by the National Organization for the Reform of Marijuana Laws (NORML)

and the Multidisciplinary Association for Psychedelic Studies (MAPS), in which the smoke

20

produced by a regular rolled cigarette, a cigarette with a cigarette filter, three different water

pipes and two different vaporisers was compared, found that cannabis smoke produced using

water pipes and cigarette filters contained 30% more tar relative to cannabinoids than did the

regular, unfiltered cigarette (Gieringer, 1996). This study used smoking conditions considered

to reflect the habits of cannabis users (59mL puff volume, 2.3s puff duration, 13s puff interval).

The differing smoking conditions prevent the direct comparison with data from this study, but

these data strengthen the conclusion that smoking cannabis via a water pipe does not confer

advantages in terms of the level of tars inhaled relative to THC.

Carbon monoxide

Carbon monoxide has a number of toxic effects on the body, the most important of which is its

impairment of oxygen transportation in the blood. Interference with tissue oxygenation would

generally be modest, but could be significant where oxygen saturation is already compromised,

particularly if this is due to cardiovascular disease when the effect of cannabis on the heart

might add stress (WHO expert working group on health effects of cannabis use, 1997). Carbon

monoxide is strongly linked with the development of coronary heart disease and it may

contribute to the development of cancers and other diseases of the respiratory tract because

of its inhibiting effect on the clearance of mucus (Winstanley et al, 1995).

The results of this study indicate that, as with tar, carbon monoxide levels in cannabis smoke

vary between cannabis samples (Table 3) and may be increased to varying extents when the

puff interval is shortened, by smoking via a water pipe rather than a cigarette (Table 4), and by

the addition of tobacco (Table 5).

It is known from studies of tobacco that the carbon monoxide yield of a given brand of

cigarettes depends on the manufacturing process, including the porosity of the paper and filter

ventilation (Kaiserman & Rickert, 1992). Studies of tobacco smoking have also found that the

absorption of carbon monoxide is more dependent on depth of inhalation than is the absorption

of nicotine (Winstanley et al, 1995), a finding that has been paralleled with cannabis smokers.

Wu et al (1988) found that, compared to smokers of tobacco cigarettes, cannabis smokers

generally inhale larger puff volumes, inspire more deeply with each inhalation, and have a

substantially longer breath-hold time post-inhalation. In a study of subjects who smoked both

cannabis and tobacco cigarettes, Wu et al (1988) determined that the cannabis smoking

21

technique was associated with a three- to four-fold increase in tar burden to the respiratory

tract, a 33% increase in tar retention, and a fivefold increase in carboxyhaemoglobin compared

to tobacco cigarettes of a similar weight. Increased breath-holding time is also a significant

determinant of tar retention and the carboxyhaemoglobin boost (Tashkin et al, 1991a). Zacny

and Chait (1991) examined the effects of systematic manipulation of breath-hold duration (0

and 20s) on the physiological and subjective response to active (2.3% THC) and placebo

(0.0% THC) cannabis in a group of ten regular cannabis smokers. They found that prolonged

breath-holding does not substantially enhance the effects of inhaled cannabis smoke. Azorlosa

et al (1995) also found that cumulative puff volume, but not prolonged breath-holding of

cannabis smoke, enhances classical subjective effects of cannabis. Thus it can be concluded

that breath-holding may increase the intake of carbon monoxide and tar with little change in

cannabinoid effects.

22

S E C T I O N 5 C O N C L U S I O N S A N D R E C O M M E N D A T I O N S

THC content of cannabis in Australia varies widely. The THC content of cannabis plant

material will contribute to the dose of THC absorbed, but the way cannabis is prepared and

smoked is also an important factor.

The amount of tar and carbon monoxide in smoke from pure cannabis smoked in cigarettes is

similar to or less than that of unfiltered tobacco cigarettes, but would be more than

commercially prepared filtered cigarettes.

This study demonstrates that, like tobacco, the composition of cannabis smoke is strongly

influenced by exactly what is being smoked and the conditions of smoking. The data reported

here indicate that intake of tar and carbon monoxide may be increased by the blending of

tobacco with cannabis, by decreasing the inter-puff interval and by smoking via a water pipe

rather than a cigarette. Other published research suggests that breath-holding, smoking

cigarettes to the end or recycling butts will also increase tar and CO load. On this basis, to

reduce respiratory risks, smokers of cannabis should smoke cannabis cigarettes (in preference

to water pipes) without tobacco, leave a butt (and not incorporate the unburnt cannabis into a

new cigarette), smoke slowly and without holding their breath.

While this and other studies suggest that smoking cannabis via a water pipe does not confer

any advantages in terms of the total amount of tar and carbon monoxide inhaled, it remains

unknown whether the water filtration has any effect on the carcinogenic potential of smoke.

Given the reports of a possible association between cannabis smoking and the development of

throat cancers (Zhang et al, 1999) this is an important area of investigation.

The limitations of the data used in this study were such that we were unable to investigate

levels of tar relative to levels of THC in cannabis smoke. This is an aspect of interest in that if

it is possible to manipulate conditions so that levels of tar are minimised relative to THC

(and/or other cannabinoids) then it may be possible to further reduce the respiratory risks of

administration via inhalation.

23

These issues are important not only in public health terms to reduce the harms due to

cannabis smoking but also for the potential therapeutic value of cannabis and cannabinoids,

particularly those therapeutic applications where inhalation may be the preferred route of

administration (for example, in the control of nausea).

In presenting the data we have alluded to the possibility of smoking temperature influencing

the release of THC and tar. Investigation of the effect of burning temperature on the release of

the various cannabinoids, tars and carbon monoxide would be of value as this is one potential

means of manipulating levels of cannabinoids relative to overall tar.

We also alluded to the possibility of cannabis cigarette butts having a filtration effect. Filters

are an important factor in controlling the tar yield of tobacco cigarettes. Investigation of the

effect of adding filters to cannabis cigarettes and water pipes in terms of levels of THC and

other cannabinoids relative to tars and carbon monoxide would indicate the feasibility of

similar strategies to reduce respiratory risks for cannabis smokers.

24

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