Mixing the Pot? 7 Ways Marijuana Interacts with Medicines

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Marijuana interactions

Marijuana is currently not approved by the U.S. Food and Drug Administration as a treatment for any medical condition, but a number of states do allow people to use the drug for medical or recreational purposes. Still, users should be aware that marijuana may interact with other prescription medications.
Although there's been limited research on marijuana's potential drug interactions, here's what doctors know about how marijuana interacts with other medications:

Viagra

Marijuana may interact with drugs, including Viagra, that are broken down by chemicals in the liver known as cytochrome P450 enzymes, according to the Mayo Clinic. That's because compounds in marijuana can inhibit these enzymes. Therefore, marijuana may prevent other drugs from being broken down properly.
As a result, people who smoke marijuana and take these drugs may have increased levels of these other drugs in their blood, which "may cause increased effects or potentially serious adverse reactions," the Mayo Clinic said.
In one case, reported in 2002 by researchers in the United Kingdom, a 41-year-old man had a heart attack after taking marijuana and Viagra together. The researchers said they could not prove that the marijuana-Viagra combination was definitely the cause of the man's heart attack; however, they did say that doctors "should be aware" of the effects of inhibiting cytochrome P450 enzymes when prescribing Viagra.

 

Warfarin

Another commonly prescribed drug that's broken down by the cytochrome P450 enzymes is the blood thinner warfarin, which is prescribed to treat and prevent blood clots. In 2009, doctors at the Cheyenne Veterans Affairs Medical Center in Wyoming reported the caseof a 56-year-old man who was admitted to the hospital with stomach bleeding after smoking marijuana frequently while taking warfarin. He went home after a week in the hospital, but then was readmitted just 15 days later with a nosebleed and bruising. He told his doctors that he smoked marijuana, and he was counseled on the potential interactions of marijuana and warfarin.
Because marijuana affects the cytochrome P450 enzymes, it may inhibit the breakdown of warfarin, leading to an increase in warfarin's effects, the report said. The man stopped smoking marijuana and did not experience further bleeding complications over the next nine months during which the researchers followed up with him.

 

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