Marijuana and Asthma: Benefits vs Risks


  • Asthma causes inflammation of the airway
  • A number of studies were conducted on humans in the 1970s
  • Studies show that THC is just as effective as traditional medications in treating asthma
  • THC relaxes the airway in both healthy and asthmatic individuals
  • Smoking marijuana still poses a risk for bronchitis, but using vaporizers or edibles reduces this risk
THC can be delivered via inhalers – Marijuana’s effects on the respiratory system are some of the most baffling findings of modern-day research. Contrary to what most might think, studies have conclusively shown that long-term cannabis use has little to no impact on the lungs.

On the other hand, those who suffer from asthma might take extra caution when it comes to smoking anything, since asthma is a potentially life-threatening disorder that can severely disrupt one’s breathing. Asthma affects approximately 250 million people worldwide and was responsible for 250,000 deaths in 2011.

But while it may be natural for asthmatics to avoid marijuana, research seems to support the opposite – that is, cannabis could be an effective treatment for the disorder.

History of Medical Marijuana

History tells us that humans have been using cannabis as a medicine for thousands of years. The earliest records come from India and China, where marijuana was recommended for the treatment of a variety of common ailments.

Interestingly, ancient medical practice in India also described the use of cannabis preparations as a treatment for asthma. Likewise, Western doctors recommended the use of cannabis for asthmatic patients up until the late 1800s.

However, it was not until the latter half of the 20th Century that scientists decided to investigate the potential of this ancient medicine as an alternative to modern-day therapies.

Human Studies – The Evidence

Numerous studies conducted in the 1970s found that THC could act as an effective bronchodilator – countering airway constriction, the primary symptom of asthma – in both healthy and asthmatic individuals.

In fact, a study published in 1977 found that THC was a stronger bronchodilator than isoproterenol, which was a common treatment for asthma at the time.

Early studies also found smoked marijuana to be effective at reversing the bronchoconstriction induced by allergic reactions or exercise in patients with asthma. Interestingly, THC seemed to elicit similar effects on the airway regardless of the route of administration.

Research from the 70s also investigated the effectiveness of using a metered-dose inhaler to deliver THC – the same method used to deliver traditional asthma medication.

A study published in 1976 showed that THC delivered via an inhaler was just as effective as Salbutamol – a widely prescribed treatment for asthma – at improving lung function in the 10 asthmatic patients that were studied. Furthermore, a study published in 1978 using the same delivery method found that THC’s bronchodilator action lasted between 3 to 6 hours – depending on the dosage – in the 5 patients that were studied.

And despite the remarkable effects observed in both studies, THC was administered at such low doses (50-200 µg) that none of the patients reported any side-effects.

Animal Studies – The Evidence

Oddly enough, research on humans ended abruptly in the 70s and has still yet to pick up again, which leaves findings from animal studies as the only source of recent evidence. Even still, animal research only serves to provide more support for the use of cannabis as a treatment for asthma.

A study published in 2008 found that administration of the synthetic cannabinoid CP55 – a compound that activates both CB1 and CB2 receptors – was able to counteract an allergic asthma-like response in guinea pigs. Cannabinoid treatment not only reduced coughing and shortness of breath, but also reduced levels of inflammatory molecules, confirming the well-known anti-inflammatory properties of medical marijuana.

Similarly, a study published in 2003 found that administration of THC or cannabinol (CBN) were both able to reduce the presence of inflammatory molecules as well as mucus overproduction in rat models of asthma.

How Does It Work?

Not only does evidence from animal research support the role of medical marijuana in treating asthma, but it also provides us with an explanation for how it works.

Interestingly, studies have identified CB1 receptors on nerve cells of the airway, suggesting a role of cannabinoid receptors in the contraction of airway muscles. What’s more, studies suggest that naturally occurring cannabinoids which mimic the effects of THC – such as anandamide – may also be able to control the contraction of airway muscles by activating CB1 receptors.

In fact, a study published in 2000 found that anandamide could relax the airway muscles and inhibit coughing induced by chemical irritants in rats.

Indeed, THC seems to provide the same therapeutic benefits as natural cannabinoids, but with a stronger and longer-lasting effect. Likewise, numerous studies have concluded that marijuana-based therapy holds much promise in the treatment of asthma, despite the fact that human studies have yet to be conducted since the 70s.


Although research seems to provide strong support for the use of medical marijuana in treating asthma, it is important to note that there are still a number of risks.

For instance, studies involving inhaler-delivered THC show that higher doses can cause bronchoconstriction in patients with asthma. Indeed, a study published in 1977 found that out of the 5 asthmatics that were studied, only 3 experienced bronchodilation, whereas 2 experienced bronchoconstriction after receiving 5-20 mg of THC, showing that dosages delivered via inhaler must be kept low in order for THC to be used as a treatment. On the other hand, studies involving smoked marijuana have yet to demonstrate similar risks.

Additionally, while studies have conclusively demonstrated that marijuana use does not increase the risk of lung cancer or impair lung function, research shows that cannabis users are still at risk of developing bronchitis.

Bronchitis is characterized by inflammation of the mucous membranes of the airway, which can lead to persistent coughing and increased mucous (phlegm) production. Bronchitis poses a particular risk to patient with asthma, since the presence of both disorders only makes symptoms worse.

However, the risk of bronchitis can be avoided by using alternative methods to ingest marijuana, such as vaporizers or edible preparations. And as research shows, THC does not need to be smoked in order to take advantage of its therapeutic benefits.

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