Marijuana is legal in many states, but that does not mean it is completely safe. Scientists are still learning how smoking weed can affect the chances of getting cancer.
Recent work at USC Keck Medicine found that people who smoke a lot of marijuana may have a higher risk of two main types of lung cancer: small‑cell and non‑small‑cell. The same researchers also saw that daily users were 3.5‑to‑5 times more likely to develop cancers in the mouth, throat, voice box, or nearby salivary glands.
How much is too much?
We still do not know the exact amount that makes the risk go up. Dr. Udelsman says that occasional use – once a week, month, or a few times a year – probably carries little danger. The problem shows up when someone smokes enough to become dependent or needs medical help because of it.
Researchers are also looking at other cancers, such as bladder and digestive‑system cancers, to see if heavy weed use plays a role.
Do edibles cause lung cancer?
Eating marijuana does not put the lungs at risk because the smoke is not inhaled. So far, studies do not link edibles to lung cancer, though we still do not know about other cancer types.
Why might marijuana smoke be harmful?
Any long‑lasting inflammation can raise cancer risk. Tobacco smoke contains over 7,000 chemicals, about 70 of which cause cancer. Marijuana smoke shares many of those same chemicals.
THC, the main psychoactive part of weed, can turn certain chemicals called PAHs into forms that irritate cells and damage DNA. When DNA is damaged, cancer can develop.
What about secondhand smoke?
There is not enough proof that breathing other people’s marijuana smoke leads to lung cancer, but inhaling the same irritating particles could still be a concern.
Which lung cancers are linked to weed?
Small‑cell lung cancer is strongly tied to tobacco, but doctors now see it in some heavy marijuana smokers too. Non‑small‑cell lung cancer also appears more often in people who smoke weed.
Does vaping marijuana raise cancer risk?
Vaping is newer than smoking, so long‑term data are limited. Vaping has been linked to serious lung inflammation, but not directly to cancer yet. Because the vapor still reaches deep lung cells, doctors suggest caution.
Occasional vs. heavy use
Occasional use likely causes only short‑term irritation that the body can repair quickly. Heavy, daily use can cause ongoing damage and may raise cancer risk, similar to tobacco smoking.
People who use a lot of marijuana should talk to a doctor. A health professional can evaluate personal risk and decide if extra screening is needed.