Quercetin and CYP Enzymes: How This Flavonoid Affects Drug Metabolism

When you take quercetin, a natural flavonoid found in apples, onions, and capers that’s often used as a supplement for inflammation and allergies. Also known as a plant-based antioxidant, it may seem harmless—but it can quietly change how your body processes many common medications. This happens because quercetin interacts with a family of liver enzymes called CYP enzymes, a group of proteins, mainly CYP3A4, CYP2C9, and CYP2D6, responsible for breaking down over 75% of all prescription drugs. Think of these enzymes as your body’s detox crew. When quercetin slows them down or speeds them up, it can turn a safe dose into a dangerous one—or make your drug stop working altogether.

For example, if you’re on a statin like simvastatin, or an antidepressant like sertraline, quercetin might block the CYP enzymes that normally clear these drugs from your system. That means more drug builds up in your blood, raising your risk of side effects like muscle pain or dizziness. On the flip side, if quercetin boosts enzyme activity, your medication might get broken down too fast, leaving you without enough of it to work. This isn’t theoretical. Studies show quercetin can inhibit CYP3A4 by up to 40% in some people, and it’s been linked to altered levels of blood thinners, immunosuppressants, and even some cancer drugs. Even if you’re not on anything heavy, mixing quercetin with common OTC painkillers like ibuprofen or naproxen could still raise your risk of stomach bleeding or kidney stress. The same goes for blood pressure meds, diabetes pills, or thyroid drugs—any drug that relies on CYP enzymes is fair game.

What makes this tricky is that quercetin doesn’t always cause problems. The effect depends on your genetics, your dose, what else you’re taking, and even what you ate that day. Some people barely notice a change. Others end up in the ER because they started taking a quercetin supplement with their warfarin and didn’t realize the connection. That’s why knowing your meds and your supplements matters. You don’t have to quit quercetin—but you do need to know if it’s safe for you. Below, you’ll find real cases and studies showing how this interaction plays out in practice: who’s at risk, which drugs are most affected, and what to do if you’re already taking both.