As cannabis use becomes more widely acceptable and gains legalization in Canada and U.S. states, concern surrounding potential interactions with common medications has surfaced. In previous studies, cannabis derivatives have been shown to inhibit P450 enzymes, but the extent of this interference has been unstudied. A new study from Washington State University is the first to demonstrate cannabis has the potential to significantly interfere with prescription drugs.1
Cannabis metabolites affect the body differently
The study, published in Drug Metabolism and Disposition, analyzed in detail the interactions between cannabinoid metabolites and hepatic P450 enzymes. These enzymes play a key role in metabolizing drugs and other chemicals in the body to avoid toxic build up.
Cannabinoids found in cannabis include mainly (-)-trans-∆9-tetrahydrocannabinol (THC), cannabinol (CBN), and cannabidiol (CBD). When consumed, these cannabinoids are converted into metabolites during the break-down process.
Compared to other cannabinoids, THC metabolites remain in the blood at higher concentrations for significantly longer.1 Thus, they have more potential to interfere with other drugs taken even days after consuming cannabis.
Cannabinoids inhibit P450 enzymes
The study used enzyme kinetic methods to analyze the effect of metabolites on P450 enzyme activity. THC, CBN, and CBD all showed competitive inhibition patterns on select P450 enzymes.
Competitive inhibition involves blockage of the active site in enzymes, directly preventing them from attaching to other drugs to break them down. Competitive inhibition of P450 enzymes can lead to a build-up of drugs to a toxic level, especially anti-cancer drugs that are metabolized by P450 enzymes. It may even lead to unintentional overdose of prescription drugs or decrease in positive effects of drugs if they’re not metabolized efficiently enough.
THC competitively inhibited the enzymes CYP1A2, CYP2B6, CYP2C9, CYP2D6, reducing their activity by approximately 50% when 10 micromolar of THC was added compared to when no cannabinoids were added. CBN competitively inhibited CYP2B6, CYP2C9, CYP2E1. The activity of each enzyme was reduced to 75%, 55%, and 80%, respectively, when 10 micromolar CBN was added. 10 micromolar of CBD competitively inhibited CYP3A4, CYP2B6, CYP2C9, CYP2D6, and CYP2E1; decreases in activity were more than 50%.1
One metabolite of cannabinoids, THC-COO-Gluc, was found to significantly inhibit key enzymes in the liver.
People with kidney disease may be at higher risk for harmful cannabinoid drug interactions
CBD was found to block three enzymes that perform 95% kidney UGT metabolism.1 According to Philip Lazarus, senior author of the study, “If you have a kidney disease or you are taking one or more drugs that are metabolized primarily through the kidney and you’re also smoking marijuana, you could be inhibiting normal kidney function, and it may have long-term effects for you.”2
“Physicians need to be aware of the possibility of toxicity or lack of response when patients are using cannabinoids,” commented Philip Lazarus. “It’s one thing if you’re young and healthy and smoke cannabis once in a while, but for older people who are using medications, taking CBD or medicinal marijuana may negatively impact their treatment.”2
More research needs to be completed to analyze the full mechanism of drug-drug interactions of cannabis on other agents in the body.
- Nasrin, S. et al. Cannabinoid Metabolites as Inhibitors of Major Hepatic CYP450 Enzymes, with Implications for Cannabis-Drug Interactions. Drug Metabolism and Disposition; 49(12): 1070-1080. Doi: 10.1124/dmd.121.000442.
- Van Dongen, J. (2021). Cannabis use could cause harmful drug interactions. EurekAlert! Accessed 16 Dec. 2021. Retrieved from https://www.eurekalert.org/news-releases/937642.
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