Marijuana and Your Risk of Lung Cancer

Medically Reviewed by Jennifer Casarella, MD on December 17, 2021
3 min read

Marijuana, both for recreation and medical use, is becoming legal in more states. Even as more people use it, health experts aren’t sure whether smoking pot raises your odds of getting lung cancer. Here’s what researchers know -- and don’t know -- about the connection.

The link between tobacco smoke and lung cancer is well-known. Studies show that marijuana smoke has many of the same harmful substances as tobacco, and often more of them. Among the hazards are:

  • Benzo(a)pyrene
  • Benz(a)anthracene
  • Phenols
  • Vinyl chlorides
  • Nitrosamines
  • Reactive oxygen species

People also smoke marijuana in a different way than tobacco, possibly posing greater danger to the lungs:

  • You usually inhale marijuana smoke deeply and hold it in, which gives the toxins more contact with your lung tissue and more chance to stick there.
  • You generally smoke a joint all the way to the end. Tar, the sticky stuff left after burning, has high levels of harmful substances, and it’s concentrated at the end of a joint.

When scientists looked at lung tissue of some people who smoke marijuana regularly, they found changes that are known to signal the future growth of cancer.

Given what scientists already know, why is it so hard to say how smoking marijuana affects your chances of getting lung cancer?

Studies that have looked for a direct link between the two have conflicting results -- some found evidence that ties marijuana to lung cancer, while other data show little to no connection.

The topic is also tough to investigate. Scientists say a few factors limit how reliable the research is.

Most of the research on marijuana dates to when it was still widely illegal. It’s hard to gather information about behavior that’s against the law. Most studies have asked people to report how often they smoked marijuana, and researchers know that these kinds of surveys, called “self-reported,” aren’t as reliable as when they collect data in other ways. That’s because people don’t remember their behavior perfectly or might underestimate or conceal how often they do something that others think is wrong.

Illegal marijuana, unlike tobacco, doesn’t have any controls on its strength or quality. People don’t use the same amount in one “dose.” That makes it hard for researchers to set standards to measure its effects.

Another problem is that many people who smoke marijuana also smoke tobacco, sometimes mixed in the same cigarette. So if they get lung cancer, it’s impossible to sort out what substance caused it.

Some marijuana smokers in the studies have been fairly young, which could skew the results. Cancers can take time to grow.

On the other hand, most people who use marijuana don’t smoke as much as a tobacco user, which could lower their odds for a problem.

Animal research suggests that some chemicals in marijuana work against tumor growth, which could explain why lung cancer isn’t showing up as often as scientists might expect in people who smoke it. The studies on this are in their early days, and researchers need to take a deeper look into this theory.

Now that marijuana is legal in more places, growers are making the product more standard and stronger. More people are smoking it, too.

Any link between marijuana smoking and lung cancer isn’t clear now, but researchers have a chance to move beyond some of the problems that have made studies unclear in the past.