A review of 55 studies found mostly neutral mental health effects from drug decriminalization and legalization—with cannabis legalization showing no consistent impact on depression, anxiety, or psychosis at the population level.
Policymakers weighing legalization proposals, mental health advocates concerned about drug policy changes, and researchers studying the public health effects of cannabis laws.
What the researchers found
As drug policies liberalize worldwide, a central concern is whether this will worsen mental health outcomes. This scoping review examined 55 studies published between 2001 and 2024 that measured non-substance-use-disorder mental health outcomes (depression, anxiety, psychosis, suicidality, overall psychological wellbeing) in relation to drug decriminalization or legalization.
The headline finding: the mental health sky has not fallen. Most studies found neutral effects—drug policy liberalization didn't significantly worsen population-level mental health outcomes. For cannabis specifically, legalization showed no consistent pattern of increased depression, anxiety, or psychotic disorders at the population level.
This doesn't mean there are no individual risks. Studies examining subgroups (heavy users, adolescents, people with pre-existing vulnerabilities) sometimes found associations with worse outcomes. But at the population level—measuring aggregate mental health across entire states or countries—legalization didn't produce the mental health crisis that some predicted.
The review distinguished between decriminalization (removing criminal penalties), legalization (establishing legal access), and commercialization (allowing retail markets), noting that these represent different policy intensities that may have different effects.
Why it matters
Mental health impact is one of the most emotionally charged arguments in the legalization debate. This systematic mapping of the evidence provides a counterweight to both extremes—neither the claim that legalization causes a mental health crisis nor the claim that it's entirely benign is well-supported by the available evidence. The nuance matters for policy.
The numbers in context
55 studies met inclusion criteria. Literature searched from 2001–2024 across 5 databases. Focused on non-SUD mental health outcomes: depression, anxiety, psychosis, suicidality, psychological wellbeing. Most studies found neutral population-level effects.
How the study worked
Scoping review following JBI guidelines and PRISMA-ScR checklist. Searched Medline, EMBASE, CINAHL, PsycInfo, and Web of Science for studies published January 2001 to December 2024. Included studies examining non-SUD mental health outcomes related to drug decriminalization, legalization, or commercialization. 55 studies met inclusion criteria.
Who was studied
55 studies (16 reviews, 39 original research articles) primarily from the US and Canada.
What this study cannot tell us
Scoping reviews map the literature without assessing study quality or conducting meta-analysis. The 55 included studies varied widely in methodology, populations, and how they measured mental health. Most evidence comes from cannabis legalization in North America—less data on other drugs or other regions. Population-level null effects can mask important subgroup effects. Only English-language studies included.
How to read the evidence
Scoping review of 55 studies—comprehensive in scope but doesn't assess individual study quality or synthesize effect sizes.
When this study was published
Published in 2025, covering studies from 2001–2024, capturing two decades of drug policy changes.
The bigger picture
This provides important context for RTHC-00163's finding that the cannabis-psychosis association disappeared after adjusting for other substance use, and for RTHC-00162's review noting stable teen use despite legalization. At the population level, the mental health evidence is more reassuring than the individual-level studies might suggest. The distinction between population-level effects (which this review covers) and individual-level risk (which studies like RTHC-00163 examine) is crucial for interpreting the overall evidence base.
Replication
Not stated in abstract.
Funding
Not reported in abstract.
Conflicts of interest
Not reported in abstract.
Questions still open
- Are there subpopulations (adolescents, people with family history of psychosis) for whom legalization does worsen mental health? Does the distinction between legalization and commercialization matter for mental health outcomes? Would longer follow-up reveal effects not yet visible?
Read the original research
Exploring the impact of drug decriminalization and legalization policies on mental health outcomes: A scoping review.
PLOS mental health, 2(10), e0000358
PLOS Mental Health is a peer-reviewed journal focusing on mental health research and policy.
Citation
Mohebbian, Mana; Najafi, Sara; Choi, You Na; Schütz, Christian; Kassam, Rosemin; Kazanjian, Arminee; Puyat, Joseph. (2025). Exploring the impact of drug decriminalization and legalization policies on mental health outcomes: A scoping review.. PLOS mental health, 2(10), e0000358. https://doi.org/10.1371/journal.pmen.0000358
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