Marijuana and the Immune System

Contributed by Brittany Cantrell Carter

Helping people stay healthy by preventing infection is a huge part of a local epidemiologist’s job. Ask an epidemiologist about the basics of disease prevention, and they may talk about handwashing, getting enough exercise, quitting cigarettes, wearing bug spray or receiving the recommended vaccinations before your trip overseas. These tips for staying healthy are widely known, but there is one tip you may not expect – avoiding marijuana use.

Marijuana has been suspected of causing immune suppression since the 1970’s. Your immune system is a complex network of cells and organs that defends your body against the millions of viruses, bacteria and parasites you encounter every day. It even fights off fungal infections and cancerous cells.

Chronic marijuana reduces your body’s natural inflammatory responseWhen you get a scrape or paper cut, you may notice redness, warmth and swelling around the area. This is inflammation – an immune response that surrounds the injury, brings helpful plasma proteins and white blood cells to the area and increases blood flow. If dangerous bacteria enter through this cut, a successful inflammatory response will prevent the spread of germs to other parts of the body. If the inflammatory response is suppressed, as occurs in long-term marijuana use, these germs can travel much farther, even all the way to your blood stream. Blood infections are rare but life-threatening.

Exposure to marijuana lowers your ability to fight certain infections. When the immune cells called macrophages (Greek for “big eaters”) encounter strange objects like bacteria, they gobble them up and digest them. Unfortunately, some bacteria know how to use our immune system against us.

Legionella pneumophila, a bacteria that causes pneumonia, can survive being swallowed whole by our macrophages and once inside, start to multiply. Most of the time Legionella infects those whose immune systems are weakened by old age or illness, but sometimes, if the person has a history of marijuana use, Legionella can also infect the young and healthy. A 2010 study looked at some severe cases of Legionella infection in young men who started using marijuana in their teenage years. Researchers discovered the macrophages in marijuana users were less capable of killing the invading bacteria, and they were also less capable of producing the chemicals needed to guide a normal immune response.

It is clear marijuana use has an impact on how people fight off infections and should be added to the list of ways marijuana negatively affects our health.


Brittany Cantrell Carter is the Environmental Epidemiologist with the Gwinnett, Newton and Rockdale County Health Departments. The Gwinnett, Newton and Rockdale County Health Departments work to protect and improve the health of those who work, live and play in their community by monitoring and preventing disease; promoting health and well-being; and preparing for disasters. For more information please visit the Health Department’s website at or call Epidemiology at 770-339-4260.

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