大麻合法化は利用と依存を増加させる可能性を示す研究 （Legalising cannabis increases use and addiction – unless it’s tightly controlled）

2026-06-18 バース大学

Possession of cannabis has been decriminalised in some countries, while commercial sales are legal in others.

＜関連情報＞

• https://www.bath.ac.uk/announcements/legalising-cannabis-increases-use-and-addiction-unless-its-tightly-controlled/
• https://www.thelancet.com/journals/lanpsy/article/PIIS2215-0366(26)00087-8/abstract

国際的な大麻政策と、大麻使用、大麻使用障害、その他の精神疾患との関連性 International cannabis policies and their association with cannabis use, cannabis use disorder, and other psychiatric disorders

Prof Tom P Freeman, PhD ∙ Rachel Lees Thorne, PhD ∙ Elle Wadsworth, PhD ∙ Tara Carney, PhD ∙ Alvaro Castillo-Carniglia, PhD ∙ Prof Magdalena Cerdá, DrPH ∙ et al.
The Lancet Psychiatry  Published: July 2026
DOI:https://doi.org/10.1016/S2215-0366(26)00087-8

Summary

Cannabis policies vary from strict prohibition to commercialised legalisation and are rapidly evolving worldwide. Here, we reviewed evidence for associations between international cannabis policy changes from 2000–25 and cannabis use, cannabis use disorder, and other psychiatric disorders. Commercialised legal markets for non-medical use in Canada and the USA were associated with increased prevalence of cannabis use and cannabis use disorder in adults and increases in cannabis potency since legalisation. There was no consistent evidence for associations between policy change and the prevalence or incidence of psychotic disorders. Commercialised legalisation was associated with an increase in hospital admissions for psychosis, and for psychotic disorders comorbid with cannabis use disorder. Poorly regulated legal access to medical cannabis, in the absence of efficacy and safety data, could increase risk of harm. Policies that limit commercialisation, such as strictly regulated legalisation of medical or non-medical supply, were not as strongly associated with cannabis use or psychiatric disorders, but long-term evaluation is needed. There was little evidence that decriminalisation of non-medical cannabis in Europe, Africa, Oceania, and Asia was associated with cannabis use or psychiatric disorders.