Cannabis Substitution in New Zealand: Large Survey Finds Reported Drops in Alcohol and Methamphetamine Use
A large New Zealand survey found that many people who used cannabis alongside other substances said they consumed less alcohol, methamphetamine, morphine, and synthetic cannabinoids after using cannabis. The findings suggest that some people may view cannabis as a substitute for other drugs—but they do not show that cannabis caused those reductions or that it is a proven treatment for substance use disorders.
The study, published in Harm Reduction Journal in 2024, analyzed responses from 23,500 participants in the New Zealand Drug Trends Survey. The online survey recruited people aged 16 and older through targeted Facebook advertising, so its participants were not a representative sample of the wider New Zealand population.
Researchers asked people who had used cannabis and another substance during the same six-month period whether cannabis had changed their use of that substance. Among respondents who reported using each drug, 60% said cannabis use was associated with less alcohol use, while 60% reported less use of synthetic cannabinoids. The corresponding figures were 44% for morphine and 40% for methamphetamine.
About seven in 10 respondents who used cannabis alongside LSD, MDMA, or cocaine said cannabis had no effect on their use of those substances. Tobacco showed a different pattern: one in five co-users said cannabis led to more tobacco use, while roughly one-third reported using less tobacco.
The results varied across demographic groups. Adults ages 21 to 35 were more likely to report that cannabis reduced their alcohol and methamphetamine use. Respondents ages 16 to 20 reported more mixed patterns, including both increases and decreases in the use of other substances. Māori participants were more likely than some other groups to report reductions in alcohol, tobacco, methamphetamine, and LSD use. Students and people living in cities were less likely to report that cannabis reduced their use of other drugs.
These patterns are consistent with the idea of drug substitution, in which a person replaces one substance with another perceived as less harmful or easier to manage. But the study measured participants’ perceptions and reported behavior at one point in time. It did not randomly assign people to use cannabis, track them over time, or establish that cannabis caused them to reduce their consumption of other drugs. Factors such as personal motivation, changing drug availability, treatment access, health concerns, and lifestyle may also have influenced the results.
The survey also cannot be used to conclude that cannabis is a safe or effective intervention for alcohol, opioid, or methamphetamine dependence. The research examined cannabis use in general, not a clinical cannabis treatment program, and it did not test whether providing cannabis would improve health outcomes. The authors called for harm-reduction policies to account for differences in age, ethnicity, lifestyle, and local drug markets rather than assuming that cannabis affects everyone in the same way.
The findings should also be considered alongside established concerns about cannabis. Public-health guidance, including the Centers for Disease Control and Prevention’s information on cannabis and adolescents, notes that early and frequent use can affect attention, memory, learning, and the developing brain, and can increase the risk of cannabis use disorder. Using cannabis with alcohol or other drugs may introduce additional risks.
For a broader view of drug-use patterns in New Zealand, readers can consult the New Zealand Drug Trends Survey and the New Zealand Ministry of Health’s drug-use statistics. Together, those resources provide context for interpreting a study that points to possible substitution among some people who use cannabis, while leaving the questions of causation, safety, and clinical effectiveness unresolved.
