CYP2C9: the enzyme that clears warfarin and NSAIDs
A drug-handling gene, not a supplement gene. Here's what your result actually tells your doctor.
CYP2C9 is the liver enzyme that does most of the work clearing the blood thinner warfarin, and it also breaks down a lot of common painkillers like ibuprofen and other NSAIDs. If your copy of this enzyme runs slower than average, the same dose of those drugs sticks around longer and hits harder. That's the entire reason CYP2C9 shows up on pharmacogenomics panels. The variant most panels check is rs1799853, which pharmacologists call CYP2C9*2. It changes one amino acid in the enzyme and slows how fast it takes warfarin apart. This page is educational. It will not tell you a dose, and you should never change a medication based on a genetics report. The point is to give you something useful to hand your doctor or pharmacist.
What CYP2C9 does
Encodes a cytochrome P450 enzyme in the liver that chemically breaks down (metabolizes) drugs so the body can clear them.
Is the main enzyme that clears S-warfarin, the more potent half of the blood thinner warfarin, by turning it into inactive hydroxy-warfarin.
Also metabolizes many NSAIDs (ibuprofen, naproxen, celecoxib), some sulfonylureas for diabetes, and phenytoin.
Comes in slower-working versions. The rs1799853 (*2) variant lowers the enzyme's activity, so warfarin clears more slowly and a smaller dose goes further.
Is a pharmacogenomics marker, meaning the result informs how a clinician doses certain drugs. It is not something a supplement can change.
Your variants, decoded
This is the classic reduced-function variant of CYP2C9. The reference letter is C (the normal, full-speed enzyme) and the variant letter is T (the *2 version, an Arg144Cys swap that slows the enzyme down). Each T copy you carry means slower warfarin clearance and, in practice, a lower dose to reach the same effect. Note on your raw data: 23andMe and some other exports read the opposite DNA strand, so they may print these as G and A instead of C and T (CC shows as GG, CT as AG, TT as AA). Same variant, just the complementary letters.
| CC | Two reference copies (*1/*1). Full-speed enzyme. Warfarin and NSAIDs clear at the typical rate. This is the most common genotype and needs no special note beyond standard care. |
| CT | One *2 copy (heterozygote). The enzyme runs slower. In a single-dose study of healthy people, one *2 copy cut S-warfarin clearance by about 25% versus CC. People with this genotype often reach a stable warfarin effect on a somewhat lower dose. |
| TT | Two *2 copies (*2/*2). The slowest of these three. Warfarin clears even less efficiently than with one copy, so dosing tends to be lower still. Less common than CC or CT. |
Genotypes are shown order-insensitively and on the forward strand; your own export may print the complementary letters — the meaning is the same.
What the research suggests
CYP2C9 is a drug-clearing enzyme, so the actionable move is informing whoever doses your medications, not buying anything. In 150 healthy single-dose subjects, carrying one rs1799853 (*2) T allele lowered S-warfarin oral clearance by about 25% versus CC, and cut formation of hydroxy-warfarin by about 45%, meaning the *2 enzyme metabolizes warfarin measurably slower. The only nutrient in this picture is vitamin K, which is warfarin's biochemical counterweight: hold your intake steady week to week (steady, not low) so the drug stays easy to dose. Talk to your doctor or pharmacist and never self-adjust a dose.
PubMed 27878474 · in 150 healthy subjects given a single warfarin dose, one CYP2C9*2 (rs1799853) allele reduced S-warfarin oral clearance by ~25% and hydroxy-warfarin formation clearance by ~45% versus *1/*1, confirming the *2 enzyme metabolizes warfarin more slowly.
Educational only — not medical advice. “General evidence” means the finding is real but the supplement’s benefit isn’t unique to your genotype.
See this matched to your own DNA — free.
Upload your 23andMe or AncestryDNA file and get your actual CYP2C9 result, plus every other actionable variant — each line cited, your file never stored.
Questions
Does a slow CYP2C9 result mean I'll have a bad reaction to warfarin?
Not on its own. It means your liver clears warfarin more slowly, so a standard starting dose can build up more than expected. This is exactly why clinicians find the result useful: it's one input into picking a safe starting dose. The person managing your medications interprets it alongside your other genes (like VKORC1), your age, and your other meds. Don't draw conclusions from the genotype alone.
Can I take a supplement to speed up my CYP2C9 enzyme?
No. Your genotype is fixed, and there's no pill that turns a *2 enzyme into a full-speed one. Anyone selling you a 'CYP2C9 booster' is selling you nothing. The honest answer is that this gene belongs in a conversation with your prescriber, not in a supplement stack.
What about vitamin K? I've read it interacts with warfarin.
It does, but through a different mechanism than CYP2C9. Warfarin works by blocking vitamin K recycling, so vitamin K from food (mostly leafy greens) is the dietary counterweight to the drug. The thing that causes trouble is big swings in intake, not the absolute amount. Keeping vitamin K steady week to week makes warfarin easier to dose. If you're on warfarin, don't suddenly start or stop a greens-heavy diet or a vitamin K supplement without telling your prescriber.
My 23andMe file shows different letters than CC/CT/TT. Did I read it wrong?
Probably not. 23andMe often reports the complementary DNA strand for this position, so you may see GG, AG, or AA instead of CC, CT, or TT. They map one to one (CC = GG, CT = AG, TT = AA). It's the same variant either way. If you're unsure how to line up your file, a pharmacist or genetic counselor can confirm it.
I'm not on warfarin or any of these drugs. Does this result matter?
It's mostly a note for your future self. If you're ever prescribed warfarin, certain NSAIDs at high doses, phenytoin, or some diabetes drugs, this result can help your clinician dose more carefully from the start. Save it and mention it if any of those come up. There's nothing to do about it day to day.