Review argues cannabis safety evidence is insufficient to support legalization, highlighting harms to mood, cognition, and driving | Research

The takeaway

A comprehensive review argued that acute and chronic cannabis use harms mood, psychiatric outcomes, cognition, driving ability, and general health, and that the public perception of cannabis as low-risk is unsupported by scientific evidence.

Read this if you want a comprehensive catalog of documented cannabis harms across multiple health domains.

High-potency recreational cannabis: high THC + low CBD = maximum risk, minimum protection

What the researchers found

The review surveyed evidence across multiple domains of cannabis harm. Acute and chronic use was associated with negative effects on mood states, psychiatric outcomes (including psychosis risk), neurocognition, driving ability, and general health.

The review noted that cannabis is "highly addictive" and that withdrawal effects can drive continued use. While CBD has demonstrated antioxidant, anticonvulsant, anti-inflammatory, and neuroprotective properties, high-potency recreational cannabis is characterized by high THC and low CBD, maximizing the harmful components.

The authors concluded that "there is insufficient evidence to support the safety of cannabis and its subsequent legalisation for recreational use" and that medical cannabis use "should be done with care."

Why it matters

As cannabis legalization advances globally, this review provides a counterpoint by comprehensively cataloging documented harms. The distinction between high-THC recreational products and CBD-rich medical preparations is important for understanding why recreational and medical cannabis may have very different risk profiles.

The numbers in context

Domains of harm: mood, psychiatric outcomes, neurocognition, driving, general health. High-potency cannabis: high THC, low CBD. CBD properties: antioxidant, anticonvulsant, anti-inflammatory, neuroprotective.

How the study worked

Narrative review covering acute and chronic effects of cannabis on psychological, cognitive, psychiatric, and physical health outcomes.

What this study cannot tell us

Narrative review that selectively presents evidence for harm. Does not systematically compare cannabis risks to those of legal substances like alcohol and tobacco. The claim that cannabis is "highly addictive" is debatable, as dependence rates are lower than for alcohol, tobacco, or opioids. The review does not adequately address dose-response relationships or differences between occasional and heavy use.

How to read the evidence

Narrative review covering multiple outcome domains. Provides a useful compilation of harm evidence but may present a one-sided perspective.

When this study was published

Published in 2017. The legalization debate has continued with additional evidence on both harms and potential benefits.

The bigger picture

The tension between cannabis's documented harms and growing social acceptance reflects a broader debate about how society weighs individual freedom against public health. This review falls firmly on the public health caution side, though critics might note that similar arguments could be made about alcohol, which remains legal.

Questions still open

Would regulated cannabis markets (with potency limits, age restrictions, and quality controls) address many of the harms cited? How do cannabis risks compare quantitatively to alcohol and tobacco? Can CBD-rich, low-THC products provide medical benefits with minimal risk?

Common questions

Is cannabis actually addictive?

The review describes cannabis as "highly addictive." Cannabis dependence is recognized in the DSM-5, with about 9% of users developing dependence (compared to ~15% for alcohol and ~32% for tobacco). The characterization depends on how "highly" is defined relative to other substances.

Is medical cannabis different from recreational?

The review distinguishes between CBD (which has therapeutic properties) and high-THC recreational cannabis. Medical formulations can be designed with specific THC:CBD ratios, while recreational products are typically high in THC and low in CBD, potentially maximizing risks.

Read the original research

Cannabis: An Overview of its Adverse Acute and Chronic Effects and its Implications.

Current drug abuse reviews, 10(1), 6-18

View on PubMed ↗Publisher’s paper ↗

Citation

Ford, Talitha C; Hayley, Amie C; Downey, Luke A; Parrott, Andrew C. (2017). Cannabis: An Overview of its Adverse Acute and Chronic Effects and its Implications.. Current drug abuse reviews, 10(1), 6-18. https://doi.org/10.2174/1874473710666170712113042