Cytochrome P450 inhibitors

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Some CYP450 inhibitors are also MAOIs.

Make sure to check our list of MAOI interactions that can be dangerous.

Cytochrome P450 inhibitors inhibit the ability of the human body to break down certain substances, potentially increasing the amount of time a substance is active in the body.

In some cases, this inhibition of how substances are broken down in the body can lead to dangerous adverse effects. Under some conditions, this can be fatal.

CYP450 inhibitors (CYP2B6 = CYP450 2B6, CYP2C19 = CYP450 2C19, etc)

  • Black Cohosh (Cimicifuga racemosa): CYP3A4[1]
  • Cannabis
    • Cannabidiol (CBD): CYP2B6, CYP2C19, CYP2D6, CYP2J2, and CYP3A4.[2][3][4][5]
    • Tetrahydrocannabinol (THC): CYP2C9, CYP2C19, CYP2D6, and CYP3A4.[3][6]
  • Fluoxetine[7]
  • Grapefruit: Bergamottin, a natural furanocoumarin in both grapefruit flesh and peel that inhibits the CYP3A4
  • Goldenseal: CYP2D6, CYP3A4 and CYP3A5[8]
  • Watercress: CYP2E1[9]
  • St. John’s Wort: CYP3A4 and CYP1A2[10]
  • Star fruit, aka carambola (from Averrhoa carambola): CYP2A6[11]
  • MAOIs


  2. Jiang, R; Yamaori, S; Okamoto, Y; Yamamoto, I; Watanabe, K (2013). "Cannabidiol is a potent inhibitor of the catalytic activity of cytochrome P450 2C19". Drug metabolism and pharmacokinetics. 28 (4): 332–8. doi:10.2133/dmpk.dmpk-12-rg-129. PMID 23318708. 
  3. 3.0 3.1 Qian, Y; Gurley, BJ; Markowitz, JS. "The Potential for Pharmacokinetic Interactions Between Cannabis Products and Conventional Medications". Journal of clinical psychopharmacology. 39 (5): 462–471. doi:10.1097/JCP.0000000000001089. PMID 31433338. 
  4. Yamaori, S; Okamoto, Y; Yamamoto, I; Watanabe, K (November 2011). "Cannabidiol, a major phytocannabinoid, as a potent atypical inhibitor for CYP2D6". Drug metabolism and disposition: the biological fate of chemicals. 39 (11): 2049–56. doi:10.1124/dmd.111.041384. PMID 21821735. 
  5. "Epidiolex (Cannabidiol) FDA Label" (PDF). US Food and Drug Administration (FDA). Retrieved June 28, 2018.  For label updates see FDA index page for NDA 210365
  6. Watanabe K, Yamaori S, Funahashi T, Kimura T, Yamamoto I (March 2007). "Cytochrome P450 enzymes involved in the metabolism of tetrahydrocannabinols and cannabinol by human hepatic microsomes". Life Science. 80 (15): 1415–9. doi:10.1016/j.lfs.2006.12.032. PMID 17303175. 
  8. Gurley BJ, Gardner SF, Hubbard MA, Williams DK, Gentry WB, Khan IA, Shah A (2005). "In vivo effects of goldenseal, kava kava, black cohosh, and valerian on human cytochrome P450 1A2, 2D6, 2E1, and 3A4/5 phenotypes". Clin. Pharmacol. Ther. 77: 415–26. doi:10.1016/j.clpt.2005.01.009. PMC 1894911Freely accessible. PMID 15900287. 
  9. Leclercq, Isabelle; Desager, Jean-Pierre; Horsmans, Yves (1998). "Inhibition of chlorzoxazone metabolism, a clinical probe for CYP2E1, by a single ingestion of watercress". Clinical Pharmacology & Therapeutics. 64 (2): 144–9. doi:10.1016/S0009-9236(98)90147-3. PMID 9728894. 
  10. Wenk M, Todesco L, Krähenbühl S (2004). "Effect of St John's wort on the activities of CYP1A2, CYP3A4, CYP2D6, N-acetyltransferase 2, and xanthine oxidase in healthy males and females" (PDF). Br J Clin Pharmacol. 57 (4): 495–499. doi:10.1111/j.1365-2125.2003.02049.x. PMC 1884478Freely accessible. PMID 15025748. 
  12. 12.0 12.1 12.2