Body and biology
What Is CYP3A4? The Enzyme Behind Many Drug Interactions
CYP3A4 · say it: SIP three-A fourAlso written: cytochrome P450 3A4, CYP 3A4, 3A4 enzyme
Short answer
CYP3A4 is a liver and gut enzyme that breaks down many medicines. Drugs or foods that block or boost it can change medicine levels.
What it means
CYP3A4 (cytochrome P450 3A4) is one of the body's main enzymes for breaking down medicines. It is found mostly in the liver and the gut wall. A large share of common medicines are processed by it, which means changes in how well it works can affect how much medicine stays in your body.
Labels mention CYP3A4 in interaction warnings. A 'strong CYP3A4 inhibitor', such as some antifungals, some antibiotics and grapefruit juice, can slow the breakdown of another medicine and raise its levels, sometimes to unsafe amounts. A 'CYP3A4 inducer', such as some anti-seizure medicines, rifampicin or St John's wort, can speed it up and make a medicine less effective. The warning is telling your doctor and pharmacist to check your full list of medicines, foods and supplements.
CYP3A4 is one member of a family of enzymes. Others, like CYP2D6 and CYP2C19, handle different medicines, and some people naturally have more or less active versions of them.
Where you may see it
- The 'Drug interactions' section of prescribing information
- Grapefruit warnings on pharmacy labels
- Pharmacist interaction checks
📄 How it looks on a report
Avoid concomitant use with strong CYP3A4 inhibitors, which may increase plasma concentrations of this drug.
🙅 What it does not mean
- It is not a medicine or a disease; it is an enzyme in your body.
- An interaction warning does not mean two medicines can never be combined; sometimes doses are adjusted.
- Grapefruit does not affect every medicine, only some.
🗒️ Questions to ask your doctor
💊 Medicines whose labels mention “CYP3A4”
Plain-English explanations of each medicine, from its official FDA label.
- Apixaban
A factor Xa inhibitor, a blood thinner medicine (anticoagulant)
- Aripiprazole
an atypical antipsychotic medicine
- Artemether and Lumefantrine
an antimalarial medicine, which is a fixed combination of two blood-stage antimalarial ingredients (artemether, an artemisinin derivative, and lumefantrine)
- Colchicine
an alkaloid medicine, a compound obtained from the autumn crocus plant (colchicum autumnale)
- Fluticasone Propionate
A corticosteroid, which is a steroid medicine, given as a nasal spray
- Lamotrigine
An anti-epileptic (seizure) medicine and mood stabilizer. The label describes it as an anti-epileptic drug of the phenyltriazine class that is chemically unrelated to other anti-epileptic drugs.
- Quetiapine
An atypical antipsychotic medicine
- Sildenafil
A phosphodiesterase-5 (PDE5) inhibitor, a medicine used to treat erectile dysfunction
- Simvastatin
a cholesterol-lowering medicine of the HMG-CoA reductase inhibitor type (often called a statin)
- Tadalafil
a phosphodiesterase 5 (PDE5) inhibitor, which is a medicine that blocks an enzyme called PDE5
🔗 Read more from trusted sources
- “CYP3A4” on MedlinePlus ↗
US National Library of Medicine
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