Cannabis is not a treatment for asthma, and smoking it is linked to more asthma, coughing and bronchitis, not less. THC can briefly widen the airways, which 1970s studies documented, but that effect does not last with regular use, and recent large studies find higher odds of asthma among people who inhale cannabis, including those who never smoked tobacco.
This page once summarized a single 1974 study that found smoked marijuana and oral THC opened the airways of people with asthma for a few hours. That finding was real, and it is why the idea of cannabis as an asthma remedy has lingered. But half a century of research since then, including a 2025 meta-analysis and a 2025 study of nearly 380,000 adults, tells a fuller story. Here is what it shows and what people with asthma should know.
The Early Studies: Short-Term Airway Opening
In the early 1970s, UCLA pulmonologist Donald Tashkin and colleagues tested cannabis in volunteers, including a 1974 study of smoked marijuana and oral THC in people with asthma. Both produced measurable bronchodilation, meaning the airways widened for a few hours. The studies were small and short, and they did not test whether regular use helps asthma over months or years.
The National Academies’ 2017 review confirmed the pattern: it found moderate evidence that smoking cannabis improves airway dynamics with acute use, but not with chronic use. A brief opening of the airways after one dose does not translate into better asthma control over time, and the smoke that delivers it irritates the lungs.
What Happens to Lungs With Regular Use
The same National Academies review found substantial evidence, its second-highest rating, that long-term cannabis smoking is associated with worse respiratory symptoms and more frequent chronic bronchitis episodes. It also found moderate evidence that those symptoms improve after people stop smoking.
The CDC says smoked cannabis can harm lung tissue, cause scarring and damage small blood vessels, and that it raises the risk of bronchitis, cough and mucus production. Cannabis smoke contains many of the same irritants and cancer-causing substances as tobacco smoke. For someone whose airways are already prone to inflammation and spasm, that matters.
Does Cannabis Cause or Worsen Asthma? New Evidence
In 2017, the National Academies found no or insufficient evidence either way on whether cannabis smoking causes asthma or makes it worse. Since then, two larger analyses have filled some of that gap.
- 2025 meta-analysis. A systematic review in BMC Pulmonary Medicine pooled eight studies and found that cannabis users had 31% higher odds of an asthma diagnosis than nonusers.
- Nearly 380,000 U.S. adults. A study in the Journal of General Internal Medicine, using national survey data from 2016 to 2020, found that daily inhaled cannabis use was associated with 44% higher odds of asthma after adjusting for tobacco. Among people who had never smoked tobacco cigarettes, the odds were 51% higher. Daily inhaled use was also linked to higher odds of COPD.
Both are observational. They show that asthma is more common among cannabis users, not that cannabis caused it, and survey studies rely on self-reported diagnoses. The direction of the evidence, however, is consistent: no large study has found that people who use cannabis have less asthma.
Research Timeline at a Glance
| Year | Study | Finding |
|---|---|---|
| 1974 | Tashkin et al., small clinical study | Smoked marijuana and oral THC briefly widened airways in people with asthma |
| 2017 | National Academies review | Short-term airway benefit only; long-term smoking linked to bronchitis; insufficient evidence on asthma |
| 2025 | Meta-analysis, 8 studies | 31% higher odds of asthma among cannabis users |
| 2025 | U.S. survey, 379,049 adults | Daily inhaled use: 44% higher odds of asthma; 51% in never-tobacco users |
What Lung Health Organizations Say
The American Lung Association cautions the public against smoking marijuana because of the risk of lung damage, states that no one should be exposed to secondhand marijuana smoke, and advises patients considering medical cannabis to talk with their doctor and use methods other than smoking. It notes that the lung effects of vaping cannabis concentrates are not well understood and may resemble those of e-cigarettes.
The American Heart Association’s 2020 statement on cannabis likewise recommends against smoking or vaping any substance, cannabis included.
Smoking vs Vaping vs Edibles for People With Asthma
- Smoking (joints, pipes, bongs) delivers hot smoke and combustion byproducts directly to irritable airways. It is the form most clearly tied to cough and bronchitis.
- Vaping avoids combustion but still delivers aerosol to the lungs, and long-term effects are not well studied. Illicit vape cartridges carry added risk from unknown additives.
- Edibles, tinctures and capsules avoid lung exposure entirely, but they do not treat asthma. They have their own risks, including delayed onset and accidental overdose.
Our Cannabis 101 section explains how these forms differ in onset and dosing.
Evidence at a Glance
| Claim | Evidence level | Source |
|---|---|---|
| THC briefly widens the airways after one dose | Moderate | National Academies 2017; Tashkin 1974 |
| Cannabis improves asthma control over time | No evidence | National Academies 2017 |
| Long-term smoking worsens cough, mucus and bronchitis | Substantial | National Academies 2017; CDC |
| Cannabis use is associated with higher odds of asthma | Moderate (observational, consistent) | Malvi 2025; Rustagi 2025 |
| Symptoms improve after quitting cannabis smoking | Moderate | National Academies 2017 |
Risks and Side Effects
- Coughing, wheezing, phlegm and bronchitis from smoke.
- Possible triggering of asthma symptoms by smoke, including secondhand smoke, especially for children in the home.
- Faster heart rate and higher blood pressure right after use. See our cannabis and heart health guide.
- Delaying proper treatment because cannabis seems to bring short-term relief.
Talk to Your Doctor
If you have asthma, keep using the inhalers and controller medicines your doctor prescribed. Cannabis is not a substitute, and no medical group recommends it for asthma. If you use cannabis, tell your doctor how and how often, since smoking it can make symptoms harder to control. If you want to cut lung exposure, not smoking is the most effective step. Seek urgent care for severe shortness of breath, chest tightness that your rescue inhaler does not relieve, or blue lips or fingertips.
For related research, browse our cannabis research section.
Cannabis and Asthma FAQ
Is weed good for asthma?
No. THC can briefly open the airways, but regular smoking is linked to worse respiratory symptoms, and large studies find higher odds of asthma among cannabis users.
Can smoking weed trigger an asthma attack?
Smoke of any kind can irritate sensitive airways, and the American Lung Association warns against smoking marijuana. The National Academies found too little research to rate cannabis as an asthma trigger specifically.
Is vaping cannabis safer for asthma than smoking?
It avoids combustion, but it still puts aerosol in the lungs, and its long-term effects are not well studied. It is not considered safe for asthma.
Can people with asthma use edibles?
Edibles avoid lung exposure, so they do not irritate the airways the way smoke does. They do not treat asthma, and dosing is harder to control. Ask your doctor first.
Does CBD help asthma?
There are no human trials showing CBD treats asthma. Interest comes from lab and animal research on inflammation, which has not been confirmed in people.
Does cannabis cause COPD?
The evidence is limited, but a large 2025 U.S. study linked daily inhaled cannabis use to higher odds of COPD after adjusting for tobacco.
For adults 21+ in legal states. General information, not medical advice. Talk to a doctor before using cannabis for a health condition.