Pubdate: 1 Oct 2000 Source: Australian and New Zealand Journal of Public Health (Australia) Copyright: 2000 Public Health Association of Australia Inc. Page: 503-508 Mail: PO Box 319, Curtin ACT 2605 Fax: (06) 282 5438 Website: http://www.pha.org.au/anzjph/anzjph.htm Authors: Wayne Hall and Wendy Swift, National Drug and Alcohol Research Centre, University of New South Wales Note: Footnote references have been placed in [brackets] to allow easier identification. THE THC CONTENT OF CANNABIS IN AUSTRALIA: EVIDENCE AND IMPLICATIONS A number of commentators in the alcohol and other drugs field have recently claimed that the THC (tetrahydrocannabinol) content of cannabis products used in Australia has increased up to 30 times over the past two decades. [1-3] The increased THC content has been attributed to the cultivation of particular cannabis strains, including hybrids of the Cannabis sativa plant such as 'skunk', and the use of hydroponic growing methods. Since THC is the psychoactive substance in cannabis that is responsible for most of its effects, [4] these claims have been used to explain an apparent increase in the adverse health and psychological effects of cannabis use among young people who are regular users of the drug. These claims have been widely and uncritically reported in the popular media and have played a prominent role in recent debates about proposed changes to legal penalties for cannabis use. They accordingly require critical analysis. In this report, we examine evidence on three linked claims: 1. That the THC content of Australian cannabis plants has increased up to 30 times. 2. That problems related to cannabis use have increased among young adults in Australia in recent years. 3. That increased THC content is the most plausible explanation of any rise in the rate of cannabis-related problems. Method To address the first question, we investigated the availability of published data on the THC content of cannabis collected by government analytical laboratories, police and health departments in New South Wales (NSW), Queensland, South Australia (SA), Victoria and Western Australia (WA). We also examined data reported in the National Illicit Drug Reports compiled by the Australian Bureau of Criminal Intelligence. We also obtained data on the THC content of cannabis in the United States (US) and New Zealand (NZ). The second question was addressed by examining available morbidity data on: the number of hospitalisations for cannabis-- related diagnoses (e.g. abuse and dependence); rates of addiction treatment for cannabis-related problems reported in national censuses of treatment agencies; and surveys of the prevalence of cannabis use among high-risk populations, such as young people in juvenile justice settings, young people with first episode psychoses, and young people who are being treated for alcohol and other drug problems. We explored alternative explanations for any increase, real or apparent, in cannabis-- related problems by undertaking secondary analyses of self-report data on cannabis use, type of cannabis consumed and method of use from the 1998 National Drug Strategy (NDS) Household Surveys (a household survey of 10,030 Australians aged 14 years and older). The unit record file of the NDS survey was purchased from the Social Science Data Archive. All data are weighted to the Australian population using weights provided with the NDS unit record file. Results Has The Average THC Content Of Australian Cannabis Plants Increased? The THC content of Australian cannabis products has not been systematically tested over the two decades in which average THC content is claimed to have increased up to 30 times. Penalties under law for cannabis offences in Australian States do not distinguish between cannabis products of differing potency, so there is no reason for police services to test THC content. Samples of seized cannabis are occasionally tested. In NSW, for example, the Division of Analytical Laboratories analysed a sample of compressed, hydroponically grown 'heads' from SA, which had a THC content of 15%. [6] Media publicity about the THC content of single samples such as this can create a false impression that these levels are typical of the cannabis products consumed in Australia. Other Australian data on cannabis samples tested for other purposes suggests that the above sample had an unusually high THC level. In 1997, a small number of cannabis seizures (leaf and head) from a number of Australian States were tested for THC content. [7] Their THC content was between 0.6-13% of plant material, with the majority of samples having a THC content of 0.6-2.5%. The mean THC content of 168 samples tested by Western Australian police between March and May 1996 was 3.8% for all samples, and 6.4% in 59 samples of 'heads'. [8] Better data have been collected on the THC potency of cannabis in the US, where a similar claim of a 30-fold increase in cannabis potency has been made. [9] The Research Institute of Pharmaceutical Sciences at the University of Mississippi has tested the THC content of cannabis seizures for the National Institute on Drug Abuse since the middle 1970s (The Potency Monitoring Project). [10,11] These data suggest that THC content in US cannabis increased between 1975 and 1998. Mikuriya and Aldrich, however, have argued that samples from the middle 1970s were not representative of cannabis consumed at that time and that the samples from the 1970s under-estimated THC potency because they were not properly stored, allowing their THC content to degrade. [12] Data from the Marijuana Potency Monitoring Project have shown an increase in the THC content of 31,000 samples from 1.2% in 1980 to 4.2% in 1997. [10] The NZ Government has tested the THC content of cannabis samples over the past two decades. These have not shown any sizeable increase in average THC content which has remained within the range of 2.0% to 4%. [13] Why Is It Believed That The THC Content Of Cannabis Has Increased? A number of factors probably explain the persistence of the belief that the THC content of cannabis plants in Australia has increased 30-fold in the absence of any supporting data. First, defenders of the claim often point to reports of single samples with unusually high THC content tested by the police. At best, such samples indicate the maximum THC content that has been achieved (assuming that there were no errors in the test results) but they do not tell us what the THC content is in the cannabis that is typically used by consumers. Second, biases in the sampling of tested cannabis are amplified by the attention that the print and electronic media give to unusually potent samples, creating a false impression that cannabis with exceptionally high THC is the norm. Third, uncontested repetition of these assertions in the media has established them as 'facts'; those who contest these claims are asked to prove that they are false rather than the (usually nameless) proponents being asked to provide evidence that they are true. Fourth, an increase in average THC content seems to explain an apparent increase in the number of cannabis users who experience problems as a consequence of their use. [14] Has The Prevalence Of Cannabis-Related Problems Increased In Australia? Data from household and school-based surveys show that cannabis use has substantially increased among young Australians over the past 20 years. [15-17] If the experience with alcohol is applicable to cannabis, then a rising prevalence of use would predict increased rates of problems. [18] There are, however, no indicators of cannabis-related mortality and morbidity that are as directly related to cannabis use as alcoholic liver cirrhosis and alcoholic psychosis are to alcohol and overdose deaths are to heroin use. Cannabis-related problems, such as cannabis-induced psychosis and cannabis dependence are contested entities that are not well recognised clinically. [19,20] A number of indicators suggest that cannabis-related problems have probably increased. National censuses of Australian addiction treatment services indicate that the proportion of persons presenting for a primary cannabis-related problem has steadily increased from 4% in 1990 to 7% in 1995. [21] A recent study of drug and alcohol services for the National Minimum Data Set Project found that 10.8% of 1395 clients sought help for a cannabis problem in 1997. [22] The number of first-time hospital admissions for cannabis abuse and dependence among young non-- Aboriginal adults in Western Australia substantially increased from 185 in 1980-1985 to 1617 in 1990-1995. [23] There are also high rates of cannabis use among subgroups of young Australians. For example, 25% of a nationally representative sample of persons with psychotic disorders in contact with services had a lifetime history of cannabis abuse and 24% were daily or near-daily cannabis users [24] compared with 2% in the general population. [25] High rates of daily cannabis use are also reported among persons with first episode psychoses, juvenile offenders before the courts and adolescents in treatment programs for alcohol and drug problems. [26-28] While we do not have good data on the prevalence ofthese disorders over time, the high prevalence of heavy cannabis use in these populations has contributed to a perception that cannabis-related problems have increased among young Australians. Alternative Explanations Of The Apparent Increase In Cannabis-Related Problems If we assume for the purposes of argument that cannabis-- related problems have increased in prevalence, it does not follow that an increase in the THC content produced by cannabis plants is the most plausible explanation. Two more plausible alternative explanations of this apparent increase in cannabis-related problems are: cannabis users more often use more potent forms of cannabis that dominate the cannabis market in Australia; and an earlier age of initiation and heavier patterns of cannabis use among young Australians have increased the prevalence of harmful patterns of cannabis use. Changing Cannabis Markets The THC content of cannabis varies between different cannabis products. Cannabis leaf contains the least THC and the flowering 'heads' contain the highest amount of THC. [29] Cannabis resin harvested from the flowering heads and compressed into hash is one of the most potent forms of cannabis. [30] Leaf, heads and hash have been available in Australia for several decades. [31] So too have more potent strains of marijuana. The Mullumbimby and the Byron Bay districts of northern NSW, for example, had a reputation for producing high-potency cannabis known as 'Mullumbimby madness' in 1981. [32] We need to distinguish between two ways in which THC content may have increased: more potent THC-producing strains of cannabis plant (e.g. 'skunk'), and more potent cannabis products derived from existing plants. The popular media give greatest attention to the first possibility; the data suggest that the latter is more plausible. Over the past two decades, a large-scale illicit cannabis industry has developed in Australia [33] to meet the demand for cannabis among a growing number of regular cannabis users. In the 1998 NDS Survey, persons who smoked cannabis weekly, or more frequently, comprised 31% of those who had used cannabis in the past year but they accounted for an estimated 96% of the cannabis consumed making conservative assumptions about their frequency of use by daily users. Regular users generally prefer the more potent forms - heads of the plant [34,35] - probably because they develop tolerance to the effects of THC. [29,36] In the 1998 NDS Survey, 94% of daily and 88% of weekly cannabis users reported that they typically smoked 'heads', 'skunk' or other potent forms of cannabis. This means that 91% of the cannabis consumed in Australia is 'heads' and other potent forms of cannabis. Changing Patterns Of Cannabis Use A major change in patterns of cannabis use among Australian adolescents and young adults is that larger numbers of younger users use more potent forms of cannabis at an earlier age. The 1998 NDS data show a strong trend towards an earlier age of initiation among younger cannabis users. One in five cannabis users (21%) born between 1940 and 1949 had initiated cannabis use by age 18, compared to 43% of those born in 1950-59, 66% of those born 1960-69 and 78% of those born in 1970-79. Earlier initiation of cannabis use increases the chances that these users will become daily or nearly daily cannabis users. [37,38] This, in turn, increases the risks of becoming dependent on cannabis and experiencing problems as a result of their use. [29,37] Levels of consumption among some adolescent cannabis users can be very high. For example, 40% of a sample of NSW juvenile offenders reported smoking [40] or more 'cones' of cannabis a week. [39] The greater expense of cannabis heads also encourages regular users to smoke them in waterpipes or 'bongs' in the belief that this maximises the delivery of THC. In the 1998 NDS Survey just over half of all persons who had used cannabis in the past year smoked 'heads' (57%) using bongs (56%). Younger users were more likely than older users to prefer bongs or pipes to joints and heads to leaf, with the trend reversed in older users. All these changes in patterns of use - earlier initiation of cannabis use, greater use of more potent cannabis products such as heads and the use of waterpipes - have probably increased the amount of THC consumed by regular cannabis users more than any speculative increase in the THC content of cannabis plants. What Are The Health Implications Of Any Increase In THC Content? Proponents of the claim that THC content has increased regard it as self-evident that it will increase the adverse health effects of cannabis use. [1,3] Critics of the claim have countered that increased THC potency may have little or no adverse effect because users are able to adjust or 'titrate' their dose of THC to achieve the desired state of intoxication. [9,12] If users were able to titrate their dose of THC, as tobacco smokers do with nicotine, [40] then the use of more potent cannabis products would reduce the amount of cannabis material that was smoked. This would marginally reduce the risks of developing respiratory diseases, the most likely adverse health effect of regular cannabis smoking. There is very little research on whether cannabis users are able to titrate their dose of THC by modifying the amount of smoke that they inhale. Some earlier studies suggested that they could [41] but more recent studies report that cannabis users have limited ability to titrate their dose of THC [42,43] so the issue has not yet been resolved. If users do not titrate their dose of THC, the health effects of using more potent cannabis products may depend upon the user's experience. Higher average doses of THC will probably increase the risk of adverse psychological effects of cannabis use (such as anxiety and panic attacks) in first-time cannabis users [29] which might discourage further use of the drug. [29] Among regular cannabis users, an increased dose of THC may increase the risks of accidents among those who drive while intoxicated, especially if cannabis use is combined with alcohol. [29,44] Research to date has not confirmed that the use of cannabis alone impairs on-road driving or increases the risks of motor vehicle accidents [44] but the use of higher doses of THC may change this risk. The use of more potent cannabis products may also increase the risk of regular cannabis users developing dependence. [30] Regular use of higher potency cannabis by persons with schizophrenia may exacerbate their illness. [19] Implications For Policy 1. We need better evidence on the THC content of cannabis. Unsubstantiated media assertions are a poor basis for public policy in any areas of public concern. 2. We need analyses of the THC content of samples of cannabis consumed by regular users. A systematic method of sampling should be used to ensure that it is not only the exceptionally potent samples of cannabis that are tested. Annual sampling of 100 to 200 samples of cannabis products would provide indications of THC content of cannabis. 3. We also need studies of the extent to which regular cannabis users are able to titrate their dose of THC. The assumed capacity of users to do so is used by some to discount concerns about any increase in the use of more potent forms of cannabis. 4. We need better assessments of the nature and extent of cannabis-related problems among adolescents and young adults. 5. More attention needs to be paid to the problems that may arise from cannabis use in health promotion efforts directed at young Australians. This could be done as part of programs that aim to prevent tobacco use and hazardous alcohol use among adolescents, [45] and as part of harm minimisation efforts to encourage less risky patterns of cannabis use among current users. [46] Conclusions The limited Australian data and data from the US and New Zealand suggest that there has been a modest increase in the THC content of cannabis plants. There probably has been an increase in the amount of THC consumed by Australian cannabis users as a result of an increased use of more potent cannabis products at an earlier age. Policies towards cannabis would be better informed if data were collected on the THC content of Australian cannabis products. Acknowledgements We would like to thank the following persons for their assistance: Keith Bedford, Greg Chesher, Paul Christie, Louisa Degenhardt, Paul Dillon, Paul Donkin, Linda Gowing, John Hannifin, Bill Lee, Simon Lenton, Michael Lynskey, Paddy Mahony, Jane Maxwell, Vince Murtagh, Helen Poulsen, James Robertson, Hari Singh, Greg Swensen and Paul Williams. BIBLIOGRAPHY: References 1. Malouf I Speech to New South Wales Drug Summit, 18 May 1999, Sydney. Proceedings of the New South Wales Drug Summit, 1999, Sydney. Retrieved November 4, 1999 available from: http://203.147.254.2/NSWDS/NSWDrugSummit.nsf/ArticleLookUp/A051899N42 2. Moffit A. Drug alert.- A guide to illicit drugs for parents. teachers, everyone. Sydney: Pan MacMillan; 1998. 3. Walters E. Marijuana: An Australian crisis. Malvern (Vic): Elaine Walters; 1993. 4. Adams IB, Martin BR. Cannabis: pharmacology and toxicology in animals and humans. Addiction 1996;91:1585-614. 5. Australian Institute of Health and Welfare. 1998 National Drug Strategy Household Survey: First results. Canberra: Australian Institute of Health and Welfare; 1999. 6. Australian Bureau of Criminal Intelligence. Australian Illicit Drug Report 1997-98. Canberra: Australian Bureau of Criminal Intelligence; 1999. 7. Gowing LR, Ali RL, White JM. Respiratory harms of smoked cannabis. Adelaide: Drug and Alcohol Services Council; 2000. DASC Monograph Research Series No.:8. 8. Western Australian Drug Abuse Strategy Office. Tends in drug purity levels in Western Australia. Perth: Western Australian Drug Abuse Strategy Office, 1999. Retrieved November 4, 1999. Available from: http://www.wa.gov.au/ drugwestaus/html/cast/frames/statdata.html 9. Zimmer L, Morgan J. Marijuana myths, marijuana facts: a review of the scientific evidence. New York: The Lindesmith Center; 1997. 10. ElSohly MA, Ross SA, Mehmedic Z, Arafat R, et al. Potency trends of D9THC and other cannabinoids in confiscated marijuana from 1980-1997. J Forensic Sci 2000;45:24-30. 11. ElSohly MA, Ross SA. Quarterly report: Potency monitoring project. Report 69: January 1, 1999-March 31, 1999. University (MS): National Center for Development of Natural Products, University of Mississippi; 1999. NIDA Contract No.:NOIDA-4-7404. 12. Mikuriya T, Aldrich MR. Cannabis 1988, old drug, new dangers: the potency question J Psychoactive Drugs 1988;20:47-55. 13. Poulsen HA, Sutherland GJ. The potency of cannabis in New Zealand from 1976 to 1996. Sci Justice. 2000;40:171-6. 14. More potent drug in use. Sutherland and St George Shire Leader 1995 August 17: 5. 15. McAllister I, Moore R, Makkai T. Drugs in Australian society: Patterns, attitudes and policies. Melbourne: Longman Cheshire; 1991. 16. Makkai T, McAllister I. Marijuana in Australia: Patterns and attitudes. Canberra: Commonwealth Department of Health and Family Services; 1997. National Drug Strategy Monograph No.: 31. 17. Lynskey M, White V, Hill D, Letcher T, et al. Prevalence of illicit drug use among youth: Results from the Australian School Students' Alcohol and Drugs Survey. Aust N Z J Public Health 1999;23:519-24. 18. Edwards G, Anderson P, Babor TF, Casswell S, et al. Alcohol policy and the public good. Oxford: Oxford University Press; 1994. 19. Hall W. Cannabis and psychosis. Drug Alcohol Rev 1998, 17: 433-44. 20. Swift W, Hall W, Teesson M. Characteristics of DSM-IV and ICD-1 0 cannabis dependence among Australian adults: results from the National Survey of Mental Health and Wellbeing. Drug Alcohol Depend. In press. 21. Torres ML, Mattick RP, Chen R, Baillie A. Clients of treatment service agencies: March 1995 Census findings. Canberra: Commonwealth Department of Human Services and Health; 1995. 22. Conroy A, Copeland J. The National Minimum Data Set Project for Alcohol and Other Drug Treatment Services: Report of the pilot study and recommended data items. Sydney: National Drug and Alcohol Research Centre; 1998. Technical Report No.: 65. 23. Patterson KM, Holman DJ, English DR, Hulse GK, et al. First-time hospital admissions with illicit drug problems in Indigenous and non-Indigenous Western Australians: an application of record linkage to public health surveillance. Aust N Z J Public Health 1999;23:460-3. 24. Jablensky A, McGrath J, Herrman H, Castle C, et al. People living with psychotic illness: An Australian study 1997-98. Canberra: Mental Health Branch, Australian Commonwealth Department of Health and Aged Care; 1999. National Survey of Mental Health and Wellbeing - Report 4. 25. Hall W, Teesson M, Lynskey M, Degenhardt L. The prevalence in the past year of substance use and ICD-10 substance use disorders in Australian adults: Findings from the National Survey of Mental Health and Well-being. Addiction 1999;94:1541-50. 26. Fowler IL, Carr VJ, Carter NT, Lewin TJ. Patterns of current and lifetime substance use in schizophrenia. Schizophr Bull 1998;24:443-55. 27. Trimboli L, Coumerlos C. Cannabis and crime: treatment programs for adolescent cannabis use. Crime Justice Bull 1998;41:1-16. 28. Spooner C, Mattick R, Noffs W The nature and treatment of adolescent substance abuse: Supplement to Monograph 26. Sydney: National Drug and Alcohol Research Centre; 1998. Monograph No.: 40. 29. Hall W, Solowij N, Lemon J. The Health and Psychological Consequences of Cannabis Use.. Canberra: AGPS; 1994. National Drug Strategy Monograph Series No.: 25. 30. Hall W, Solowij N. The adverse effects of cannabis use. Lancet 1998;352:161116. 31. Senate Select Committee on Drug Trafficking and Drug Abuse. Report from the Senate Select Committee on Drug Trafficking and Drug Abuse. Part 1: Report. Canberra: Commonwealth Government Printing Office; 1971. Parliamentary Paper No.: 204. 32. Brouwer S. Mullumbimby madness. Australian Playboy 1981 August. 33. Queensland Advisory Committee on Illicit Drugs. Cannabis and the law in Queensland: A discussion paper. Toowong (Qld): Queensland Criminal Justice Commission; 1993. 34. Reilly D, Didcott P, Swift W, Hall W Long-term cannabis use: Characteristics of users in an Australian rural area. Addiction 1998;93:837-46. 35. Swift W, Hall W, Copeland J. Characteristics of long-term cannabis users in Sydney Australia. Eur Addict Res 1998;4:190-7. 36. Compton D, Dewey W, Martin B. Cannabis dependence and tolerance production. Adv Alcohol Subst Abuse 1990;9:129-47. 37. Fergusson DM, Horwood LJ. Early onset cannabis use and psychosocial adjustments in young adults. Addiction 1997;92:279-96. 38. Kandel DB, Davies M. Progression to regular marijuana involvement: phenomenology and risk factors for near daily use. In: Glantz M, Pickens R. editors. Vulnerability to drug abuse. Washington (DC): American Psychological Association; 1992:211-53. 39. Salmelainen P The correlates of offending frequency: A study of juvenile theft offenders in detention. Sydney: New South Wales Bureau of Crime Statistics and Research; 1995. 40. Herring RI, Jones RT, Bachman J, Mines AH. Puff volume increases when low-nicotine cigarettes are smoked. Br MedJ 1981;283:187-9. 41. Perez-Reyes M, DiGuiseppi S, Davis KH, Scnidler VH, et al. Comparison of marijuana cigarettes of three different potencies. Clin Pharmacol Ther 1982;31:617-24. 42. Matthias P, Tashkin DP, Marques-Magallanes JA, Wilkins IN, et al. Effects of varying marijuana potency on deposition of tar and D-THC in the lung during smoking. Pharmacol Biochem Behav 1997;58:1145-50. 43. Wu TC, Tashkin DP, Rose JE, Djahed B. Influence of marijuana potency and amount of cigarette consumed on marijuana smoking pattern J Psychoactive Drugs 1988;20:43-6. 44. Smiley A. Marijuana: on road and driving simulator studies. In: Kalant H, Corrigal W, Hall W, Smart R,editors. The Health Effects of Cannabis. Toronto: Addiction Research Foundation; 1999:172-94. 45. Hall W, Nelson J. Public Perceptions ofthe Health and Psychological Consequences of Cannabis Use. Canberra: AGPS; 1995. National Drug Strategy Monograph No.: 29. 46. Swift W, Copeland J, Lemon S. Cannabis and harm reduction (Harm Reduction Digest 8). Drug Alcohol Rev 2000;19:101-12. - --- MAP posted-by: Richard Lake