What you may have heard
Marijuana use causes cancer.
What science tells us
Marijuana is the name given to the dried buds and leaves of the cannabis plant; it goes by many names, including pot, grass, cannabis, weed, and hemp. Marijuana plants come in many different strains with different levels of active compounds, and effects can vary based on how deeply and how long the user inhales; as a result, each user’s experience is very different.
Delta-9-tetrahydrocannabinol (THC) causes the “high” reported by marijuana users and can also help relieve pain and nausea, and reduce inflammation (ACS). Cannabidiol (CBD) can be used to help treat seizures, reduce anxiety and paranoia, and can counteract the high caused by THC (ACS).
Marijuana can pose some harm to users. The most common effects of marijuana are euphoria, decreased control over movement, disorientation, and sometimes anxiety, paranoia, suicidality, or psychosis (DFCI). Smoked marijuana delivers THC and other cannabinoids to the body, but also delivers harmful substances to those close by (ACS). Marijuana smoking can cause chronic bronchitis and problems with learning, memory, and attention.
Both cannabis and cannabinoids may be addictive. Symptoms of withdrawal from cannabis may include being easily annoyed or angered, trouble sleeping, unable to stay still, hot flashes, nausea, or cramping (NCI).
The US Drug Enforcement Administration (DEA) lists marijuana as a Schedule I controlled substance, even though some states have legalized its purchase and use, it cannot be legally prescribed, possessed, or sold under federal law. However, the use of marijuana to treat some medical conditions is legal under state laws in many states.
There is much we still do not know about marijuana use because its potential cancer effects are poorly studied and it is still characterized as an illegal substance by the US DEA. The categorization of marijuana as an illegal substance limits the amount of research and the types of research that scientists can do. More human research studies are needed to see the effects of marijuana over time.
Laboratory Evidence/Supporting Evidence
Animal studies have reported the effect of marijuana. One study found that marijuana reduced the size of prostate tumors, which differed based on the dose and length of the treatment. However, further studies are needed to confirm this result (Singh et al.).
IARC Carcinogen Classification: Not classified
How to reduce your risk
The American Cancer Society recommends that any decisions about pain and symptom management with marijuana use should be made between a patient and their doctor, balancing evidence of benefit and harm to the patient, the patient’s preferences and values, and any laws and regulations that may apply. The mode of marijuana consumption may also affect cancer risk, with smoking (burning) of marijuana producing potential cancer-related substances.
There is not enough evidence to say if marijuana use is linked to cancer, but marijuana use may pose other harms to users.
Learn More From These Trusted Sources
American Cancer Society (ACS): Marijuana and cancer
Dana-Farber Cancer Institute (DFCI): Marijuana and cancer
National Cancer Institute (NCI): Cannabis
Published: June 25, 2021
Verified/updated: August 22, 2022