Published summary: 2026-03-07
Where the evidence converges
Meta-analysis of 8 studies found cannabis users had 31% higher odds of asthma diagnosis than non-users, with consistent results across sensitivity analyses
Strong evidence · 1 studies
Included studies were observational, so causation cannot be established. The analysis could not distinguish between different modes of consumption (smoking vs. vaping vs. edibles). Moderate heterogene
The 2019 EVALI outbreak caused 805 lung injury cases and 12 deaths
Moderate evidence · 12 studies
Based on limited number of strong-evidence studies.
Where questions remain
A 1978 medical review identified cannabis as promising for glaucoma and asthma but flagged cardiovascular risks during exercise and preliminary concerns about lung and immune effects
Moderate evidence · 27 studies
As a narrative review from 1978, it reflects limited evidence available at that time. The cannabis landscape has changed dramatically in terms of product potency, consumption methods, and the volume o
A major 1986 pharmacological review found cannabis's greatest health concern was its impact on youth development, while finding no proven brain damage and limited physical dependence in adults
Moderate evidence · 27 studies
Reflects evidence available through the mid-1980s. Cannabis potency, usage patterns, and the volume of research have all changed dramatically. The review's reassurance about lung effects preceded mode
Daily marijuana smoking produced tobacco-like respiratory symptoms, but COPD would likely require 4-5 joints daily for 30+ years
Moderate evidence · 27 studies
Narrative review format without systematic quality assessment. Cancer risk estimates were based on case reports, not controlled epidemiological studies. The COPD threshold estimate was extrapolated fr
Comprehensive review finding solid evidence for cannabinoids in nausea and appetite, emerging evidence for pain and spasticity, and weak evidence for glaucoma and asthma, while advocating for non-smoked delivery methods
Moderate evidence · 27 studies
As a narrative review rather than a systematic review or meta-analysis, the study selection and interpretation reflected the author's judgment. Long-term pharmacokinetic data and drug interaction info
Research gaps
- Only 2 randomized controlled trials exist out of 135 studies — most evidence is observational or from reviews.
- Sex-specific differences in this area remain understudied.
- Long-term prospective studies tracking outcomes over 5+ years are largely absent from the literature.
- Research on diverse populations (different ages, ethnicities, and medical backgrounds) remains limited.
Key studies
Cannabis Users Had 31% Higher Odds of Having Asthma in a Meta-Analysis
Cannabis is the third most widely used psychoactive substance globally, and smoked cannabis delivers irritants similar to tobacco smoke. This meta-analysis provides the strongest pooled evidence to date that cannabis use is associated with higher odds of having asthma.
Vaporized cannabis did not help breathing or exercise endurance in people with severe COPD
Some people with COPD use cannabis hoping it will help their breathing, partly based on old studies showing bronchodilatory effects in other populations. This rigorous trial found that those earlier findings do not translate to advanced COPD. The null result is itself important information, as it he
Pilot test of whether cannabis extract helps breathlessness in COPD patients
Breathlessness in COPD is difficult to treat. If cannabinoids can change the subjective quality of breathlessness without suppressing respiratory drive, they could fill a treatment gap where opioids carry respiratory depression risk.
Cannabinoid Vaping Products Contain High Concentrations and Potentially Toxic Byproducts
The 2018 Farm Bill created an unregulated market for hemp-derived vaping products. While EVALI highlighted vitamin E acetate risks, this review identifies additional toxic mechanisms that may explain ongoing lung injury reports even after VEA awareness increased.
Cannabis Concentrate Vaping Produces Substantial Toxic Byproducts
Cannabis concentrates are the fastest-growing market segment, but research on their specific inhalation risks has significantly lagged their widespread use.
People Hospitalized for Cannabis Use Disorder Had Nearly 3x the Death Risk Over 5 Years
This is one of the largest studies to quantify mortality risk associated with cannabis use disorder severe enough to require emergency or hospital care. The findings suggest CUD is a marker for serious health vulnerability, even after accounting for other mental health and substance use conditions.
How the research developed
Pre-2000
5 studies published. Predominantly observational and review studies.
2000–2009
6 studies published. Predominantly observational and review studies.
2010–2014
7 studies published. Includes 1 RCTs.
2015–2019
35 studies published. Includes 1 RCTs, 1 strong-evidence studies.
2020–present
82 studies published. Includes 1 meta-analyses, 11 strong-evidence studies.
How this summary was assembled
This consensus synthesizes 135 peer-reviewed studies: 1 meta-analyses (1%), 2 randomized controlled trials (1%), 51 observational studies (38%), 39 reviews (29%), 12 case studies (9%), 30 other study types (22%). Studies span from the earliest available research through 2025. Evidence strength ratings reflect study design, sample size, and replication across multiple research groups.
These counts describe the source summary at publication. They may differ from the current library.