Marijuana and Lung Health
The American Lung Association is concerned about the health impacts of marijuana use, especially on lung health. We caution the public against smoking marijuana because of the risks it poses to the lungs.
Scientists are researching marijuana now, and the American Lung Association encourages continued research into the effects of marijuana use on lung health.
The health effects of marijuana are determined in large part by how it's consumed.
Marijuana is most commonly smoked using pipes, bongs, paper-wrapped joints, blunts and other devices including those that heat or vaporize marijuana.
Marijuana can also be consumed through dozens of different products including e-cigarettes, candy, brownies and other baked goods, capsules, beverages and many more.
While this statement focuses on marijuana and lung health, it's important to note that there are other health concerns outside the lungs attributed to marijuana use that are not addressed here, including neurological and cognitive effects.1,2
Additionally, there are significant public health concerns associated with pediatric poisonings caused by accidental ingestion of edible marijuana products.3
Smoke is harmful to lung health. Whether from burning wood, tobacco or marijuana, toxins and carcinogens are released from the combustion of materials. Smoke from marijuana combustion has been shown to contain many of the same toxins, irritants and carcinogens as tobacco smoke.4-7
Beyond just what's in the smoke alone, marijuana is typically smoked differently than tobacco. Marijuana smokers tend to inhale more deeply and hold their breath longer than cigarette smokers, which leads to a greater exposure per breath to tar.8
Secondhand marijuana smoke contains many of the same toxins and carcinogens found in directly-inhaled marijuana smoke, in similar amounts if not more.
5 While there is no data on the health consequences of breathing secondhand marijuana smoke, there is concern that it could cause harmful health effects, especially among vulnerable children in the home.
Additional research on the health effects of secondhand marijuana smoke is needed.
Lung Health and Marijuana Smoke
Smoking marijuana clearly damages the human lung. Research shows that smoking marijuana causes chronic bronchitis and marijuana smoke has been shown to injure the cell linings of the large airways, which could explain why smoking marijuana leads to symptoms such as chronic cough, phlegm production, wheeze and acute bronchitis.4,9
Smoking marijuana has also been linked to cases of air pockets in between both lungs and between the lungs and the chest wall, as well as large air bubbles in the lungs among young to middle-aged adults, mostly heavy smokers of marijuana.
However, it's not possible to establish whether these occur more frequently among marijuana smokers than the general population.4
Smoking marijuana can harm more than just the lungs and respiratory system—it can also affect the immune system and the body's ability to fight disease, especially for those whose immune systems are already weakened from immunosuppressive drugs or diseases, such as HIV infection.4,9
Smoking marijuana hurts the lungs' first line of defense against infection by killing cells that help remove dust and germs as well as causing more mucus to be formed. In addition, it also suppresses the immune system.
These effects could lead to an increased risk of lower respiratory tract infections among marijuana smokers, although there is no clear evidence of such actual infections being more common among marijuana smokers.
4,9 However, frequent marijuana-only smokers have more healthcare visits for respiratory conditions compared to nonsmokers.10
Studies have shown that smoking marijuana may increase the risk of opportunistic infections among those who are HIV positive, although it does not seem to affect the development of AIDS or lower white cell counts.4,9
Another potential threat to those with weakened immune systems is Aspergillus, a mold that can cause lung disorders. It can grow on marijuana, which if then smoked exposes the lungs to this fungus.4 However, it rarely causes problems in people with healthy immune systems.
There is little known on the potential lung health effects of inhaling marijuana or products made from it through routes other than smoking. However:
- Use of «vape-pens» to inhale cannabis concentrates or liquids may have similar respiratory health effects as e-cigarette use.
- «Dabbing» (inhaling flash-vaporized cannabis concentrates) may also cause respiratory problems.
The American Lung Association encourages continued research into the health effects of marijuana use, as the benefits, risks and safety of marijuana use for medical purposes require further study. Patients considering using marijuana for medicinal purposes should make this decision in consultation with their doctor, and consider means of administration other than smoking.
- Smoking marijuana clearly damages the human lung, and regular use leads to chronic bronchitis and can cause an immune-compromised person to be more susceptible to lung infections.
- No one should be exposed to secondhand marijuana smoke.
- Due to the risks it poses to lung health, the American Lung Association strongly cautions the public against smoking marijuana as well as tobacco products.
- More research is needed into the effects of marijuana on health, especially lung health.
See our public policy position on marijuana and lung health.
Working out with weed
Some sportspeople claim that using cannabis enhances their athletic performance.Credit: Rido/Shutterstock
The stereotypical image of a cannabis smoker is someone who sprawls on the sofa for hours surrounded by a haze of smoke and half-eaten snacks.
The scene is played up for laughs in films, but social psychologist Angela Bryan thought it could be cause for concern.
After all, cannabis is known to increase appetite and aid relaxation, which might put people at risk of health conditions such as obesity, says Bryan, who is at the University of Colorado Boulder.
Part of Nature Outlook: Cannabis
But digging into health trends revealed the opposite. Nationwide US studies report that, compared to non-users, cannabis users actually have a lower prevalence of obesity1. Intrigued, she began to investigate.
Earlier this year, her team surveyed more than 600 cannabis users living in US states where the drug is legal about their exercise habits, among other health factors2. Four five respondents said that they use marijuana right before or after exercising.
And those users spent more minutes per week exercising than users who didn’t mix the two. “We were shocked,” Bryan says.
Her findings and those of others suggest that using cannabis before or after working out could be common. But scientists know very little about the effects cannabis could have on exercise.
A handful of studies were conducted decades ago, but since then laboratories in the United States have found it difficult to run controlled cannabis studies because of federal restrictions.
Instead, researchers are turning to surveys and anecdotal reports to piece together the biological mechanisms by which cannabis might affect physical activity.
A survey says
In Bryan’s survey, about 70% of respondents who used cannabis before working out said doing so made exercising more enjoyable. People who use cannabis might say that taking the drug makes any activity more fun, but Bryan suggests that in the case of exercise there are specific chemical interactions at play.
Consider a runner’s high, the feeling of euphoria that kicks in when some people reach a sweet spot in their workout.
The experience has been attributed to the release of chemicals in the brain called endorphins, but solid evidence of this is wanting. For instance, endorphins are thought to give a pleasurable feeling because they activate opioid receptors.
But researchers have found that people who take opioid-blocking drugs before exercising can still achieve states of bliss during a workout3.
An alternative suggestion is that exercise-induced euphoria originates in the endocannabinoid system.
A 2003 study4 found elevated levels of the endocannabinoid molecule anandamide in the blood of volunteers after they ran or cycled in a lab.
Because cannabis targets these same endocannabinoid receptors, Bryan speculates that the drug might allow users to “jumpstart” those pleasurable feelings.
She stresses that direct evidence connecting cannabis to runner’s high remains to be found. But nevertheless, she says, people say they enjoy exercise with cannabis, which could create a positive feedback loop that motivates them to go back to the gym. “If something feels good,” she says, “you’re going to want to do it again.”
Another way in which cannabis could encourage exercise is by aiding recovery, Bryan says. In her survey, 77% of people who use cannabis alongside exercise said that it helps with recovery. Again, researchers haven’t done controlled studies looking at cannabis and recovery. So, for now, Bryan says, “we have to kind of guess the mechanisms that we know.”
What researchers do know is that intense physical activity puts stress on the body. It triggers a flood of chemicals known as cytokines, some of which inflame muscles, that manifests as soreness the next day. Cannabis might modulate this inflammation — but potentially in multiple conflicting ways.
Bryan explains that although cannabidiol (CBD), a non-psychoactive component of cannabis, has been shown to suppress pro-inflammatory cytokines, the psychoactive part, tetrahydrocannabinol (THC), stimulates both pro- and anti-inflammatory cytokines. In other words, CBD could limit the feeling of sore muscles, whereas THC could help to both prevent and trigger the discomfort.
Some studies suggest that THC can also help to manage pain5, which might also boost recovery, she says.
Bryan’s team found that the survey respondents who used cannabis alongside exercise tended to be younger and male. Meanwhile, a survey, the results of which are unpublished, conducted on social media by Humboldt State University in Arcata, California, which targeted people who use cannabis with exercise, had roughly an equal number of male and female participants.
Olympic snowboarder Ross Rebagliati tested positive for the cannabinoid tetrahydrocannabinol in 1998.Credit: Frank Gunn/The Canadian Press/AP
Led by Whitney Ogle, a physical therapist and cannabis researcher at Humboldt, the survey of 126 people uncovered cannabis use before all sorts of physical activity — 55 activities in total, ranging from archery to waterskiing.
Aside from sheer enjoyment, people in the Humboldt survey reported numerous other benefits of combining cannabis with exercise.
They thought that cannabis increased their focus, concentration and mind–body awareness — something that elite athletes have also reported6, although scientists have yet to come up with possible mechanisms for these effects.
Ogle’s survey also asked participants something the Colorado team’s survey did not: did people have negative experiences after combining cannabis and exercise? About 40% of respondents reported adverse effects, which included elevated heart rate and being too high to continue with their workout, Ogle says.
The biggest limitation of the survey by the Colorado team, Bryan says, is that it didn’t include a non-user control group.
The researchers polled people from states such as Colorado, California and Washington, which already have higher levels of physical activity than does the country as a whole, so it’s hard to tell whether cannabis motivated people to exercise more than is typical in those states.
Soon, researchers could have access to populations with a wider range of activity levels. “The good news for researchers is that states are legalizing crazy,” Bryan says. Eleven US states and the District of Columbia have approved recreational marijuana use, and 33 states allow medical marijuana.
Evidence versus anecdote
Although survey data are valuable for designing experiments, they will not provide the evidence that researchers such as Bryan crave. Currently, anecdotes concerning cannabis and exercise far outnumber controlled studies of the relationship, but that’s not to say that no one has tried.
In 2018, researchers at McMaster University in Hamilton, Canada, scoured the literature for studies of marijuana’s effect on athletic performance that included a control group. Only three small studies made the cut7.
Conducted between 1975 and 1986 in people under the age of 35, two of the studies in the review7 had participants exercise before and after smoking cannabis. The third study was purely observational.
In areas such as workout times, heart rate and blood pressure, the studies mostly recorded either no difference from the control groups, or negative effects.
The sole positive finding, from a study with 24 participants, was an increase in forced exhalation, or the amount of air participants could exhale after taking a deep breath.
On the basis of the studies’ low sample size and quality — two studies used marijuana containing about 1–2% THC, much lower than recreational levels in the United States, which in 2014 averaged around 12% — the authors concluded that the “effects of marijuana on athletic performance remain unclear”.
Despite the lack of evidence that cannabis enhances performance, the concern led the World Anti-Doping Agency (WADA) to ban cannabis use during competitions when it assumed responsibility for the list of prohibited substances in 2004.
According to WADA, which is based in Montreal, Canada, and is affiliated with the International Olympic Committee (IOC), the drug meets all the criteria for being banned.
As well as having potential to enhance performance, it poses health risks to athletes, and is illegal in many parts of the world.
Olivier Rabin, WADA’s senior science director, explained the agency’s reasoning for the cannabis ban in a 2011 paper8 co-authored by a researcher from the US National Institute on Drug Abuse. Although he acknowledges that the scientific evidence is shaky, Rabin says that the “wealth of testimonies” from athletes who admit to using cannabis to enhance their performance can’t be ignored.
These accounts — mainly unpublished reports made to WADA’s doping support hotlines — have come from a number of sports, he says.
For example, goalkeepers in football say that cannabis increases their focus, helping them drown out the many distractions in the stadium.
Athletes in other sports, such as skateboarding and skiing, say that cannabis reduces competition anxiety that can hinder performance.
Rabin says that athletes seem to be able to “titrate” their cannabis use to get just the results they want; he ns it to drinking just enough alcohol to be sociable at a party. Cannabis might not enhance performance at all doses and in all situations, he says, but its use could be advantageous in some circumstances.
More from Nature Outlooks
Over the past several years, as perceptions of marijuana have evolved in society, so too has WADA’s stance on the drug. In 1998, before WADA officially took on its anti-doping duties, Canadian snowboarder Ross Rebagliati was stripped of his Olympic gold medal after officials detected 17.8 nanograms per millilitre of THC in his system.
Rebagliati’s medal was reinstated soon after, on the basis that the IOC had not listed cannabis as a banned substance. In 2013, WADA raised the level of cannabis allowed in urine samples from 15 nanograms per millilitre to 150 nanograms per millilitre.
Rabin says that this higher level will focus WADA’s anti-doping efforts on active users of cannabis instead of infrequent users who aren’t trying to enhance their performance.
Even as public acceptance of marijuana grows, researchers are finding it difficult to fully investigate cannabis’s impact on physical activity because of the restrictions on cannabis research. Federal policy requires that scientists submit to an application process that can take six months to one year.
On approval, researchers are only allowed to use government-provided cannabis with levels of THC that are often lower than those of cannabis available to the public. “Until regulations change,” Ogle says, “we’re really thwarted from being able to do really good research that we know the public wants and needs.
Researchers are coming up with creative ways to get around these rules.
Some of Bryan’s collaborators in Colorado have created a mobile lab — essentially, a renovated van that can be parked outside participants’ homes — to test users after they have consumed their own product.
Because testing takes place off-campus, scientists aren’t subject to campus restrictions on cannabis. With these kinds of creative approach, Bryan says, scientists could start investigating the effects of cannabis on specific aspects of exercise such as inflammation.
But the question she’d most to answer is probably the most difficult one: does cannabis directly influence people’s decision to exercise? “To me,” says Bryan, “that’s the most interesting question out there.”
Nature 572, S14-S15 (2019)
Marijuana is a shredded, green-brown mix of dried flowers, stems, and leaves from the plant Cannabis sativa. A stronger form of marijuana, called hashish (hash), looks brown or black cakes or balls. The amount of THC (the active ingredient) in marijuana and marijuana products has increased greatly over the years.
Marijuana is usually rolled and smoked a cigarette (joints or doobies), or put in hollowed-out cigars (blunts), pipes (bowls), or water pipes (bongs). Recently, it has become increasingly popular for people to inhale marijuana or stronger marijuana extracts using a vaporizer (called «vaping» or «dabbing»). Some people mix it into food or brew it as a tea.
There is also «synthetic marijuana» — manmade drugs that are chemically similar to THC — that can be dangerously strong. Names for these drugs include «K2,» «Spice,» and «Herbal Incense.» They can be so potent that overdose deaths have happened.
The main active chemical in marijuana is THC (delta-9-tetrahydrocannabinol). When someone smokes marijuana, THC goes from the lungs into the bloodstream. From there, it ends up in the brain and other organs.
THC connects with a receptor on nerve cells in the brain. The marijuana «high» results from THC's effects on the nerve cells that control sensory perception and pleasure.
THC also connects with receptors on nerve cells in other parts of the brain that affect thinking, memory, coordination, and concentration. This can cause unwanted side effects, including:
- trouble thinking and problem solving
- problems with memory and learning
- loss of coordination
- distorted perception
These side effects are temporary, but they can make it dangerous to do things drive while under the influence of marijuana.
People also might notice other short-term side effects of using marijuana, such as:
- an increased appetite
- feeling lightheaded or drowsy
- a decrease in inhibitions
Research has found that people who use marijuana over a long period of time can have more lasting side effects. For example:
Changes in the brain. Marijuana can affect the parts of the brain that play a role in our ability to remember, multitask, and pay attention.
Fertility issues. Animal studies suggest that using a lot of marijuana might be linked to decreased sperm count in men and delayed ovulation in women. Pregnant women who use marijuana might be more ly to have babies with developmental and behavioral problems.
Respiratory problems. People who smoke marijuana a lot can develop problems with the respiratory system — more mucus, a chronic cough, and bronchitis.
Immune system problems. Using marijuana a lot might make it harder for the body to fight off infections.
Emotional problems. People who use a lot of marijuana are more ly to say they notice signs of depression or anxiety. If someone has a condition schizophrenia or bipolar disorder, marijuana can sometimes make symptoms worse.
Here are a few ways marijuana use could affect you:
Criminal charges. Marijuana laws can be confusing. Some states are changing their laws to make it legal to have small amounts of marijuana in some situations ( when it's prescribed for medical use).
Some have even made recreational use of marijuana by adults (over 21) legal.
But there are conflicting federal laws against using, growing, or selling marijuana — and people caught with it could face charges, including jail time.
Career problems. People charged under marijuana laws may end up with criminal records that hurt their plans for college or finding a job.
Drug testing. These days, employers often test for drug use as part of the hiring process. Marijuana can show up on a drug test for several weeks after it was last used. So people who use marijuana may find they don't get a job they want. Some companies do routine drug tests on employees, so people who use marijuana can lose their jobs.
Medical Use of Marijuana
Food and Drug Administration (FDA) has approved pills containing THC or other cannabinoids (chemicals similar to THC) as a way to help relieve pain, nausea, muscle stiffness, or problems with movement.
There's still a lot of discussion about the medical use of marijuana, though. THC and other cannabinoid pills are only available in some states and require a doctor's prescription.
At the moment, there's not enough research to say for sure if smoking marijuana is any more helpful than taking THC or other cannabinoids as a pill. Scientists are still studying this.
What If I Want to Quit?
People who use marijuana for a while can have withdrawal symptoms when they try to give it up. They may feel irritable, anxious, or depressed; have trouble sleeping; or not feel eating.
Marijuana withdrawal can be a bit caffeine withdrawal: It's usually worse a day or two after someone stops using marijuana. After that, withdrawal symptoms gradually decrease. They're usually gone a week or two after the person no longer uses the drug.
Marijuana can be addictive. About 1 in 10 people who use the drug regularly can develop a «marijuana use disorder.» These people can't stop using marijuana even though it causing problems in their lives. This is much more ly to happen in people who start using marijuana before age 18.
If you or someone you know wants to stop using marijuana but has trouble quitting, it can help to talk to a counselor. Studies suggest that a combination of individual counseling and group therapy sessions is the best approach for stopping marijuana use.