What you carry at this position in your DNA and what research says about it.
Medication Response: 9/10 evidence, 10 publications.
You're viewing every possible genotype for this variant.
None of these is your result. Use the genotype toggle to compare them, then sign up and upload your DNA to see which one is yours.
Sample genotype (not yours): G/G
Typical Response to Common Medications
This genotype is associated with standard metabolism of warfarin, clopidogrel, and omeprazole. Standard dosing guidelines are typically effective without genetic adjustments.
What this genotype means: Typical warfarin response; Typical antiplatelet response to clopidogrel; Normal metabolism of proton pump inhibitors.
Sample genotype (not yours): A/A
Significantly Altered Response to Blood Thinners
This genotype is linked to significantly slower metabolism of warfarin and clopidogrel. This is associated with substantially greater sensitivity to warfarin and with poor activation of clopidogrel.
What this genotype means: High sensitivity to warfarin; Poor clopidogrel antiplatelet efficacy; Slower metabolism of omeprazole.
Sample genotype (not yours): G/A
Altered Response to Blood Thinners
This genotype is linked to slower metabolism of certain medications, including warfarin and clopidogrel. This is associated with greater sensitivity to warfarin and with reduced activation of clopidogrel.
What this genotype means: Increased sensitivity to warfarin; Reduced clopidogrel antiplatelet efficacy; Slower metabolism of omeprazole.
Gene function and biological role
Gene Function: The CYP2C gene cluster on chromosome 10 contains several cytochrome P450 genes, including CYP2C9, CYP2C19, CYP2C8, and CYP2C18 [1]. These genes encode enzymes that are primarily responsible for metabolizing a wide variety of clinically important medications [1]. Among these, CYP2C9 and CYP2C19 play critical roles in processing anticoagulants and antiplatelet drugs [2]. Variations within this cluster can significantly alter enzyme activity, leading to differences in how individuals process medications [2].
Variant Impact: The rs12777823 variant is an intergenic single nucleotide variation located within the CYP2C gene cluster on chromosome 10 [2]. Although it does not directly alter a protein sequence, it is highly associated with the expression and function of neighboring CYP2C enzymes [2]. This variant is in strong linkage disequilibrium with the CYP2C19*2 allele, which is a well-known non-functional variant of the CYP2C19 gene [3]. Consequently, rs12777823 serves as a powerful genetic marker for predicting drug metabolism, particularly in populations of African descent [2].
Key Insight: This variant is a critical marker for warfarin dosing in African Americans, improving dose prediction by 21 percent when included in standard algorithms.
Location: CYP2C19. Chromosome 10 · 10q23.33 · 94.6 Mb
Estimated prevalence by population
Global 65.9%; European 72.0%; African 56.3%; East Asian 47.3%; South Asian 44.3%; Americas 73.9%; Ashkenazi 75.3%; Finnish 66.6%; Middle Eastern 81.9%; Amish 66.9%.
Estimated GG genotype frequency.
Global 30.2%; European 25.7%; African 37.5%; East Asian 42.9%; South Asian 44.5%; Americas 24.2%; Ashkenazi 23.0%; Finnish 30.0%; Middle Eastern 17.2%; Amish 29.8%.
Estimated GA genotype frequency.
Global 3.9%; European 2.3%; African 6.2%; East Asian 9.7%; South Asian 11.2%; Americas 2.0%; Ashkenazi 1.8%; Finnish 3.4%; Middle Eastern 0.9%; Amish 3.3%.
Estimated AA genotype frequency.
Showing effects for G/G genotype
Pharmacogenomics
Anticoagulant & Blood Thinner Response
Warfarin Sensitivity. Evidence: 9/10. Source: PMID 23755828. Typical Sensitivity.
Clopidogrel Response. Evidence: 3/10. Source: PMID 19706858. Typical Efficacy.
Organ Systems
Digestive & Gut Disorders
Omeprazole Metabolism. Evidence: 5/10. Source: PMID 38637968. Typical Metabolism.
Showing effects for A/A genotype
Warfarin Sensitivity. Evidence: 9/10. Source: PMID 23755828. High Sensitivity.
Clopidogrel Response. Evidence: 3/10. Source: PMID 19706858. Poor Efficacy.
Omeprazole Metabolism. Evidence: 5/10. Source: PMID 38637968. Slower Metabolism.
Showing effects for G/A genotype
Warfarin Sensitivity. Evidence: 9/10. Source: PMID 23755828. Increased Sensitivity.
Clopidogrel Response. Evidence: 3/10. Source: PMID 19706858. Reduced Efficacy.
What this genotype means for the people who carry it
Sample genotype: GG (Homozygous)
Enzymatic activity in the CYP2C cluster remains typical for those carrying two copies of the common G allele [1]. Sensitivity to the blood thinner warfarin is typical for this genotype [1]. Normal activation of the antiplatelet drug clopidogrel is also maintained, providing typical protection against cardiovascular events [2]. Standard doses of proton pump inhibitors like omeprazole are processed normally [3]. This is the reference pattern against which the other genotypes are compared in the published literature [1].
Typical warfarin response; Typical antiplatelet response to clopidogrel; Normal metabolism of proton pump inhibitors.
Sample genotype: AA (Homozygous)
Pronounced reduction in the metabolism of several key medications is associated with carrying two copies of the A allele [1]. In people taking warfarin, this genotype is associated with markedly increased sensitivity to the drug, producing a stronger anticoagulant effect than non-carriers at the same amount [1]. This association is highly critical for personalized dosing in patients of African descent [2]. Furthermore, poor activation of clopidogrel can lead to a higher risk of adverse cardiovascular events due to inadequate platelet inhibition [3]. Slower clearance of omeprazole is also expected [4].
High sensitivity to warfarin; Poor clopidogrel antiplatelet efficacy; Slower metabolism of omeprazole.
Sample genotype: GA (Heterozygous)
Reduced metabolism of several common medications is associated with carrying one copy of the A allele [1]. For those taking the anticoagulant warfarin, carriers show increased sensitivity to the drug, reaching a stronger anticoagulant effect than non-carriers at the same amount [1]. This genetic effect is particularly prominent and clinically validated in populations of African ancestry [2]. Additionally, reduced activation of clopidogrel may decrease its effectiveness in preventing blood clots [3]. Slower metabolism of proton pump inhibitors like omeprazole has also been observed [4].
Increased sensitivity to warfarin; Reduced clopidogrel antiplatelet efficacy; Slower metabolism of omeprazole.
Variants with shared genetic architecture
rs28399504 · CYP2C19 Gene · Chr 10 · Drug Metabolism
rs41291556 · CYP2C19 Gene · Chr 10 · Clopidogrel Response
rs12248560 · CYP2C19 Gene · Chr 10 · Drug Response and Cancer Risk
Pharmacogenomics knowledge for personalized medicine.
Content updated August 2026.
ReadYourDNA provides educational interpretation of DNA data you already have. It is not diagnostic, not a substitute for professional medical advice, diagnosis, or treatment, and is not intended to diagnose, treat, cure, or prevent any disease. Talk to a clinician before acting on any result.
Raw DNA Data Reports for 23andMe & AncestryDNA · About ReadYourDNA · FAQ · Methodology & Science · Pricing · Support and complaints · Legal & Contact · Health Traits · Pharmacogenomics · Carrier Status · Variant Explorer · The Human Karyotype · Privacy Policy · Terms of Service · Accessibility · Consumer Health Data Privacy · Your Privacy Choices · Editorial Standards · Your Data, Checkable · Sample Report · ReadYourDNA and Promethease compared · What is inside a 23andMe raw data file · What is inside an AncestryDNA raw data file · What a chatbot can and cannot do with your raw DNA file · Where a raw DNA file can still be uploaded in 2026
Written, maintained and operated by Martin Pechhacker, sole proprietor, Vienna, Austria. Trade register GISA 40064420. support@readyourdna.com