The THC content of cannabis in Australia: evidence and implications

Objective: To examine evidence on three claims that: 1) the THC content of Australian cannabis plants has increased up to 30 times; 2) problems experi enced by cannabis users have increased in Australia in recent years; and 3) an increase in THC content is the most likely explanation of any increase in cannabis-related problems. Methods: These claims were assessed by examining data: 1) on THC potency in Australia, the United States and New Zealand; 2) on cannabis-related probl ems; and 3) from the 1998 National Drug Strategy Household Survey on patter ns of cannabis use. Results: 1) Published data do not show a 30-fold increase in THC potency of cannabis but show a more modest increase in the US. 2) There is suggestive evidence of an increase in cannabis-related problems among people seeking treatment for alcohol and drug problems, juvenile offenders and young adult s with psychosis. 3) There are two other more plausible explanations for th ese reportedly higher rates of cannabis-related problems among adolescents and young adults: (i) more potent forms of cannabis ('heads') are more wide ly used; and Iii) cannabis users are initiating cannabis at an earlier age, thereby increasing the prevalence of harmful patterns of use. Conclusions: There has probably been a modest increase in the THC content o f cannabis, but changing patterns of cannabis use have probably made a larg er contribution to any increase in rates of cannabis-related problems among young Australian adults. Implications: Better data on the THC content of cannabis, the extent of can abis-related problems and the ability of users to titrate the dose of canna bis would contribute to more informed debate.