A large-scale study of nearly 4,000 cannabis users in Japan has found little evidence to support the gateway drug hypothesis, further debunking the misinformed assumption that cannabis leads to harder substance use.
The research, published in the journal Neuropsychopharmacology Reports, revealed that cannabis was typically the third most commonly used substance reported by participants.
“Cannabis use in Japan typically follows alcohol and tobacco, and rarely leads to further drug use,” the researchers concluded after analysing data from 3,900 community-based cannabis users.
Tobacco (48.1%) and alcohol (42.3%) were the most common first substances used, while cannabis was most frequently reported as the third substance (68.2%). Crucially, 54.7% of individuals who used cannabis as their third substance reported no further transition to other substances.
The odds of using other substances after cannabis were remarkably low: 1.25 for alcohol, 0.77 for tobacco, 0.08 for methamphetamine, and 0.78 for any illegal drug.
“These findings challenge the gateway hypothesis in the Japanese context,” said lead researcher Dr Yuji Masataka from St. Marianna University School of Medicine.
The research comes at a significant time for Japanese drug policy, as the country recently toughened its cannabis laws in December 2024, introducing criminal penalties for cannabis use for the first time and increasing prison sentences to up to seven years.
The study suggests that shared psychosocial vulnerabilities, rather than a pharmacological gateway effect, may better explain patterns of drug use. Japan’s strict drug regulations and social stigmas may influence usage behaviours differently than in Western contexts.
The anonymous online survey was conducted in January 2021, recruiting participants through social media platforms. The majority of respondents were male (81.5%), with the largest age group being 20-24 years (28.9%).
Whilst 10.4% of cannabis users reported experience with methamphetamine, considerably higher than the estimated 0.5% in the general Japanese population, the researchers noted this doesn’t establish causality.
The authors propose that Japan’s regulatory environment may contribute to cannabis and other illegal drugs circulating within the same black market, increasing users’ exposure to various substances through policy rather than pharmacological effects.
The study acknowledged several limitations, including recruitment bias through cannabis advocacy platforms and reliance on self-reported data. The researchers called for larger-scale cohort studies involving the general population to overcome these constraints.
The findings add to growing international evidence that debunks the gateway drug hypothesis, with the researchers noting that “strong causal evidence for progression to other substances is limited.”
A separate study using brain imaging technology found no evidence that cannabis use causes the brain changes that would support the gateway drug hypothesis. Published in January 2025, the research examining the neurological basis of the gateway theory found that cannabis consumption did not produce the specific brain alterations that would make users more susceptible to harder drugs.
The study’s findings suggest that any observed progression from cannabis to harder substances is likely due to environmental and social factors or pre-existing mental health conditions, rather than biological changes in the brain caused by cannabis use itself.
