What you carry at this position in your DNA and what research says about it.
Drug Response and Cancer Risk: 8/10 evidence, 19 publications.
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Sample genotype (not yours): C/C
Typical Drug Clearance and Breast Cancer Risk
Normal enzyme activity ensures standard processing of common medications. Standard estrogen breakdown maintains typical baseline susceptibility to breast cancer.
What this genotype means: Standard processing of common antidepressants; Typical response to acid reflux medications; Baseline susceptibility to breast cancer.
Sample genotype (not yours): C/T
Faster Drug Clearance and Lower Breast Cancer Risk
Elevated enzyme activity accelerates the breakdown of several common medications, potentially reducing their effectiveness. Accelerated estrogen clearance is linked to a lower risk of breast cancer.
What this genotype means: Faster clearance of certain antidepressants and acid reflux drugs; Enhanced activation of clopidogrel; Reduced risk of breast cancer.
Sample genotype (not yours): T/T
Ultrarapid Drug Clearance and Lower Breast Cancer Risk
Highly elevated enzyme activity rapidly clears many common medications, which may significantly lower their efficacy. Rapid estrogen breakdown provides a protective effect against breast cancer.
What this genotype means: Rapid clearance of certain antidepressants and acid reflux drugs; Highly efficient activation of clopidogrel; Reduced risk of breast cancer.
Gene function and biological role
Gene Function: The CYP2C19 gene encodes a key member of the cytochrome P450 enzyme superfamily, which is primarily active in the liver. This enzyme plays a critical role in the detoxification of foreign compounds and the metabolism of many clinically important drugs [1]. It is responsible for breaking down or activating diverse medications, including antiplatelet agents, antidepressants, and proton pump inhibitors [2]. Additionally, the enzyme contributes to the breakdown of endogenous substances, such as estrogen hormones [3]. Genetic variations in this gene are highly common and significantly alter how rapidly these substances are cleared from the body [4].
Variant Impact: The rs12248560 variant is a single nucleotide change located in the promoter region of the CYP2C19 gene [5]. This specific change creates a new binding site for GATA transcription factors, which increases the expression of the gene [2]. As a result, the variant leads to elevated levels of the CYP2C19 enzyme and defines the well-known CYP2C19*17 star allele [4]. This increased function causes an ultrarapid or rapid drug metabolizer phenotype, accelerating the clearance of many medications [1].
Key Insight: This variant acts as a genetic accelerator, speeding up the breakdown of both common medications and natural hormones like estrogen, which simultaneously alters drug efficacy and lowers breast cancer risk.
Location: CYP2C19. Chromosome 10 · 10q23.33 · 94.8 Mb
Estimated prevalence by population
Global 64.2%; European 60.8%; African 60.7%; East Asian 98.1%; South Asian 70.1%; Americas 75.2%; Ashkenazi 61.9%; Finnish 66.4%; Middle Eastern 59.1%; Amish 54.1%.
Estimated CC genotype frequency.
Global 31.6%; European 34.3%; African 34.4%; East Asian 1.9%; South Asian 27.3%; Americas 23.1%; Ashkenazi 33.6%; Finnish 30.1%; Middle Eastern 35.6%; Amish 38.9%.
Estimated CT genotype frequency.
Global 4.2%; European 4.8%; African 4.9%; East Asian < 0.1%; South Asian 2.7%; Americas 1.8%; Ashkenazi 4.6%; Finnish 3.4%; Middle Eastern 5.3%; Amish 7.0%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Cancer & Oncology
Breast Cancer
Breast Cancer. Evidence: 5/10. Source: PMID 18521743. Typical Risk.
Pharmacogenomics
Anticoagulant & Blood Thinner Response
Clopidogrel Response. Evidence: 8/10. Source: PMID 21392617. Typical Response.
Antidepressant & Psychiatric Drug Response
Antidepressant Response. Evidence: 3/10. Source: PMID 21172166. Typical Response.
Organ Systems
Digestive & Gut Disorders
Acid Reflux Drug Response. Evidence: 3/10. Source: PMID 19136640. Typical Response.
Showing effects for C/T genotype
Breast Cancer. Evidence: 5/10. Source: PMID 18521743. ~23% Lower Risk.
Clopidogrel Response. Evidence: 8/10. Source: PMID 21392617. Enhanced Response.
Antidepressant Response. Evidence: 3/10. Source: PMID 21172166. Lower Efficacy.
Acid Reflux Drug Response. Evidence: 3/10. Source: PMID 19136640. Lower Efficacy.
Showing effects for T/T genotype
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Standard enzyme levels result in typical processing speeds for a wide variety of medications, including antidepressants and acid reflux treatments [1]. Standard clearance rates mean that standard clinical dosing guidelines are generally effective [2]. Estrogen hormones are also processed at a typical rate, maintaining a standard baseline risk for hormone-sensitive conditions like breast cancer [3]. Standard antiplatelet therapy with clopidogrel is processed normally, providing expected protection against blood clots [4].
Standard processing of common antidepressants; Typical response to acid reflux medications; Baseline susceptibility to breast cancer.
Sample genotype: CT (Heterozygous)
Elevated enzyme activity accelerates the clearance of several common medications, which can reduce their therapeutic levels in the body [1]. Conversely, the antiplatelet drug clopidogrel is activated more efficiently, offering enhanced protection against blood clots [3]. Accelerated breakdown of estrogen hormones is associated with a twenty-three percent reduction in breast cancer risk, an effect that is even more pronounced during long-term hormone therapy [4].
Faster clearance of certain antidepressants and acid reflux drugs; Enhanced activation of clopidogrel; Reduced risk of breast cancer.
Sample genotype: TT (Homozygous)
Highly elevated enzyme activity rapidly clears many common medications, which may significantly lower their efficacy [1]. Antidepressants and proton pump inhibitors are cleared so quickly that standard doses may fail to achieve therapeutic effects [2]. Conversely, the antiplatelet drug clopidogrel is activated very efficiently, offering enhanced protection against blood clots [3]. Rapid breakdown of estrogen hormones is associated with a twenty-three percent reduction in breast cancer risk, an effect that is even more pronounced during long-term hormone therapy [4].
Rapid clearance of certain antidepressants and acid reflux drugs; Highly efficient activation of clopidogrel; Reduced risk of breast cancer.
Variants with shared genetic architecture
rs28399504 · CYP2C19 Gene · Chr 10 · Drug Metabolism
rs41291556 · CYP2C19 Gene · Chr 10 · Clopidogrel Response
rs12777823 · CYP2C19 Gene · Chr 10 · Medication Response
CPIC: Clinical Pharmacogenetics Implementation Consortium of the Pharmacogenomics Research Network.
CYP2C19*17 is associated with decreased breast cancer risk.
Development and validation of T-ARMS-PCR to detect CYP2C19*17 allele.
Pharmacogenetics of antidepressant response.
Content updated August 2026.
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