Laws allowing adults to use marijuana are becoming more common across the U.S. The drug is now legal for medical use in 39 states and for recreational use in 24 states.
All told, nearly 62 million Americans (22% of the population) reported using marijuana in 2022, up from 28 million in 2009. The state-by-state percentages range from 34% of adults in Vermont to 14% in Alabama. In Texas, where medical use of the drug is legal, 15% said they'd used the drug.
Researchers have found that legalization increases the use of marijuana by 20%. But even as more people use it, health experts aren't sure whether smoking or vaping marijuana increases a person's risk of getting lung cancer.
"Scientific research often requires significant time to gather conclusive evidence," says Dr. Min Kim, a thoracic surgeon at Houston Methodist. "It took several decades for researchers to move from suspecting cigarettes as a cause of lung cancer to definitively proving it. Similarly, while we know that marijuana contains chemicals that could potentially cause cancer, it may take time for scientific research to provide conclusive evidence on the matter."
Many people believe that smoking marijuana is less harmful than smoking tobacco. These are very different substances, but both can have profound effects on the body, especially on the lungs.
Marijuana and tobacco: What's the difference?
Before we examine the differences between marijuana and tobacco, it's important to know that smoke — no matter the source — is harmful to the lungs and can cause long-term breathing issues and even the development of cancer.
The most obvious difference between tobacco and marijuana is the key component of each. Tobacco produces significant amounts of nicotine, an addictive stimulant that increases dopamine levels in the brain, resulting in feelings of pleasure and reward. Marijuana contains substantial amounts of tetrahydrocannabinol (THC), a chemical that can cause changes in mood, thoughts and perception of reality.
We've known for half a century that smoking tobacco can cause cancer. The American Cancer Society reports that individuals who smoke cigarettes are 25 times more likely to develop lung cancer than people who never smoked.
While we don't have similar proof or statistics for marijuana, we do know that the smoke from marijuana contains many of the same toxins, irritants and carcinogens as tobacco smoke. However, the research is mixed on which one contains more of these chemicals.
One other potential difference between the two is the inhalation technique. Marijuana smokers tend to inhale more deeply and hold their breath longer, resulting in a longer exposure to the smoke.
Limited research on marijuana and cancer
Studies that have investigated a link between marijuana and lung cancer have so far resulted in weak or conflicting results. Why is it so hard to prove that smoking marijuana affects your lung cancer risk? There are a few reasons.
First, most of the studies looking into the topic have been small, in part due to the drug's limited legality. Marijuana also isn't as strictly regulated for strength and quality as tobacco, making it difficult for researchers to determine a standard "dose." Another challenge is that some marijuana consumers also smoke tobacco, making it difficult to figure out the true cause of any diseases that develop.
"We're going to need more time and more data to determine any relationship between marijuana use and lung cancer," says Dr. Kim. "We know that marijuana contains chemicals that have the potential to cause cancer. Animal studies suggest there may be a relationship between marijuana use and cancer risk. However, translating findings from these animal studies into large-scale population studies that provide conclusive evidence could take considerable time."
It's important to note that even if a link is determined to exist between smoking marijuana and lung cancer, not all marijuana users will develop the disease. Many factors can influence a person's cancer risk, including genetics and lifestyle.
How else can marijuana affect your lungs?
While the jury is still out on a potential link between marijuana and lung cancer, research has shown that marijuana use can damage the lungs in other ways.
Smoking marijuana increases your risk of developing chronic bronchitis. This inflammation of the airways can lead to coughing, increased mucus production and difficulty breathing. The smoke from marijuana also can weaken your immune system, making you more susceptible to lung infections.
Aspergillus is a type of mold that can grow on marijuana plants and can cause infection if introduced into the lungs through smoking. This can be especially serious for people with weakened immune systems.
Vaping, whether tobacco or marijuana, has been marketed as a safer alternative to smoking, but research is showing that's not entirely true. In fact, vaping can cause EVALI, e-cigarette or vaping use-associated lung injury, a serious lung condition that causes lung scarring and inflammation. The illness is connected to vitamin E acetate, a substance sometimes added to vaping liquids. If you have asthma, smoking or vaping can make the condition worse. (Related: Does Vaping Cause Lung Cancer?)
It's also important to remember that marijuana doesn't just affect the lungs. It's also been associated with other health concerns, including an impact on neurological and cognitive function.
The importance of future research
More people than ever are smoking or vaping marijuana — and that number is likely to grow. Unfortunately, many people believe it is a safer alternative to smoking tobacco. In fact, there's no evidence to support that viewpoint.
We know that marijuana smoke contains many of the same harmful chemicals as tobacco smoke and that smoking or vaping it can cause damage to the lungs. Researchers are working hard to understand any potential ties more fully between marijuana smoke and lung cancer.
"Although we cannot definitively say that smoking marijuana causes lung cancer at this time, I strongly encourage people to avoid inhaling substances that may contain potential carcinogens." says Dr. Kim.
