What you carry at this position in your DNA and what research says about it.
Medication Sensitivity: 9/10 evidence, 33 publications.
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Sample genotype (not yours): C/C
Typical Medication Metabolism
Normal CYP2C9 enzyme activity allows for standard processing of many common medications. There is no genetically increased risk of side effects from warfarin or NSAIDs.
What this genotype means: Normal clearance of warfarin and NSAIDs; Standard drug dosing applies.
Sample genotype (not yours): C/T
Slightly Slower Medication Metabolism
One copy of the variant reduces CYP2C9 enzyme activity, slowing down the clearance of blood thinners and NSAIDs. This can increase the risk of side effects like bleeding.
What this genotype means: Increased sensitivity to warfarin; Slightly higher risk of NSAID-related GI bleeding.
Sample genotype (not yours): T/T
Significantly Slower Medication Metabolism
Two copies of the variant significantly reduce CYP2C9 enzyme activity, leading to slow clearance of several common drugs. This markedly increases the risk of drug toxicity and bleeding.
What this genotype means: High sensitivity to warfarin and NSAIDs; Increased risk of drug-induced side effects.
Gene function and biological role
Gene Function: The CYP2C9 gene encodes an enzyme that is a major member of the cytochrome P450 superfamily [1]. This enzyme plays a critical role in the liver by metabolizing many clinically important drugs, including anticoagulants, nonsteroidal anti-inflammatory drugs, and anticonvulsants [1]. Variations in this gene can significantly alter how quickly or slowly these medications are cleared from the body [2]. When enzyme activity is altered, standard drug doses can become ineffective or toxic [2].
Variant Impact: The rs1799853 variant, commonly known as the CYP2C9*2 allele, is a missense mutation that changes the amino acid arginine to cysteine at position 144 of the enzyme [3]. This specific structural change reduces the enzyme's catalytic activity, leading to a decreased ability to metabolize substrate drugs [3]. Because the enzyme processes medications more slowly, drugs can accumulate in the bloodstream [2]. This slow clearance significantly increases the risk of drug-related side effects and toxicity [2].
Key Insight: This variant reduces the liver's ability to clear common pain relievers like ibuprofen, which can unexpectedly increase the risk of stomach irritation and bleeding.
Location: CYP2C9. Chromosome 10 · 10q23.33 · 94.9 Mb
Estimated prevalence by population
Global 83.4%; European 76.3%; African 95.4%; East Asian 99.9%; South Asian 92.4%; Americas 81.4%; Ashkenazi 74.8%; Finnish 77.8%; Middle Eastern 74.0%; Amish 71.8%.
Estimated CC genotype frequency.
Global 15.6%; European 22.1%; African 4.6%; East Asian 0.1%; South Asian 7.5%; Americas 17.6%; Ashkenazi 23.4%; Finnish 20.8%; Middle Eastern 24.0%; Amish 25.8%.
Estimated CT genotype frequency.
Global 1.0%; European 1.6%; African 0.1%; East Asian < 0.1%; South Asian 0.2%; Americas 1.0%; Ashkenazi 1.8%; Finnish 1.4%; Middle Eastern 1.9%; Amish 2.3%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Pharmacogenomics
Anticoagulant & Blood Thinner Response
Warfarin Sensitivity. Evidence: 9/10. Source: PMID 19300499. Typical Metabolism.
Adverse Drug Reactions
NSAID Bleeding Risk. Evidence: 3/10. Source: PMID 19422321. Typical Risk.
Cardiovascular Drug Response
Blood Pressure Drug Response. Evidence: 8/10. Source: PMID 12359989. Typical Response.
Cardiovascular & Metabolic
Coagulation & Clotting
Blood Clot Risk. Evidence: 5/10. Source: PMID 28750087. Typical Risk.
Showing effects for C/T genotype
Warfarin Sensitivity. Evidence: 9/10. Source: PMID 19300499. ~20% Slower Clearance.
NSAID Bleeding Risk. Evidence: 3/10. Source: PMID 19422321. Increased Risk.
Blood Pressure Drug Response. Evidence: 8/10. Source: PMID 12359989. Stronger Response.
Blood Clot Risk. Evidence: 5/10. Source: PMID 28750087. Increased Risk.
Showing effects for T/T genotype
Warfarin Sensitivity. Evidence: 9/10. Source: PMID 19300499. ~40% Slower Clearance.
NSAID Bleeding Risk. Evidence: 3/10. Source: PMID 19422321. Higher Risk.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Standard genetic makeup at this position results in fully functional CYP2C9 enzymes [1]. Medications such as the blood thinner warfarin and common NSAIDs like ibuprofen are metabolized at a normal rate [1]. This means standard dosing guidelines are typically appropriate, and there is no elevated genetic risk of gastrointestinal bleeding from these drugs [2]. Additionally, response to blood pressure medications like irbesartan and oral contraceptives is expected to be typical [3] [4].
Normal clearance of warfarin and NSAIDs; Standard drug dosing applies.
Sample genotype: CT (Heterozygous)
One copy of the T allele reduces CYP2C9 enzyme activity by approximately 20% [1]. This slower clearance means medications like warfarin remain in the bloodstream longer, increasing sensitivity and the risk of bleeding [1]. Common pain relievers like ibuprofen and other NSAIDs are also processed more slowly, which can elevate the risk of gastrointestinal irritation or bleeding [2]. However, this genotype is associated with a more favorable blood pressure response to the medication irbesartan [3]. There is also a slightly increased risk of blood clots when using combined oral contraceptives [4].
Increased sensitivity to warfarin; Slightly higher risk of NSAID-related GI bleeding.
Sample genotype: TT (Homozygous)
Two copies of the T allele lead to a reduction of approximately 40% in CYP2C9 enzyme activity [1]. This slow metabolism causes drugs like warfarin to accumulate, producing a stronger anticoagulant effect and a higher bleeding risk [1]. The risk of gastrointestinal bleeding from NSAIDs like ibuprofen is also significantly higher [2]. For diabetes management, this genotype may show a poorer response to sitagliptin but a better response to sulfonylureas [3] [4]. Additionally, there is an increased risk of venous blood clots when taking combined oral contraceptives [5].
High sensitivity to warfarin and NSAIDs; Increased risk of drug-induced side effects.
Variants with shared genetic architecture
rs1057910 · CYP2C9 Gene · Chr 10 · Medication Sensitivity
rs28371685 · CYP2C9 Gene · Chr 10 · Medication Metabolism
rs28371686 · CYP2C9 Gene · Chr 10 · Medication Response
Upstream and coding region CYP2C9 polymorphisms: correlation with warfarin dose and metabolism.
Impaired (S)-warfarin metabolism catalysed by the R144C allelic variant of CYP2C9.
Risk prediction of developing venous thrombosis in combined oral contraceptive users.
Content updated August 2026.
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