Ask An Expert: Long-term Marijuana Use

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Ask An Expert: Long-term Marijuana Use

Question:

What are the medical effects of smoking cannabis for a long period of time?

Answer:

It has been difficult to study long-term risks of marijuana use, because it is illegal to dispense this drug to subjects in a formal study. However, doctors accept some effects of long-term marijuana use based upon reasonable evidence. These include:

• Chronic lung disease: Smoking three or four marijuana cigarettes per day has been identified as an approximate equivalent of smoking 20 cigarettes (one pack of regular nicotine-based cigarettes), in terms of its effects on chronic lung injury. There is a higher pollutant exposure within the lungs for marijuana cigarettes as opposed to regular cigarettes. Chronic lung disease from marijuana includes chronic bronchitis, emphysema, or both (chronic obstructive pulmonary disease, or COPD).

• Cancers: Marijuana use appears to increase the risk of cancer in the head and neck and is likely to contribute to lung cancer.

• Heart attack: Heart attack risk is higher immediately after smoking marijuana.

• Effects on fertility and sex drive: In men, marijuana affects the function and quantity of sperm, reduces testosterone levels, reduces sexual drive, can stimulate male breast enlargement, and causes impotence. In women, period cycles can become shorter and fertility can be reduced. Spontaneous leakage of milk from the breasts (when a woman is not breast-feeding) has been attributed to marijuana in many cases. Marijuana does cross the placenta and is thought to reduce the birth weight of babies.

• Psychiatric effects: Marijuana use is associated with higher rates of depression and schizophrenia in later adult years. Also, there is strong evidence that suggests marijuana use can lead to the abuse of other substances.

• Long-term memory and attention skills: Users of marijuana averaging 10 years of use have poorer brain function than do short-term users, even after they have discontinued the drug.

Mary Pickett, M.D., is a lecturer for Harvard Medical School and an assistant professor of medicine at Oregon Health & Science University in Portland, OR. At OHSU, she practices general internal medicine and teaches medical residents and students.

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Last updated:	January 24, 2007