What you carry at this position in your DNA and what research says about it.
Medication Response: 7/10 evidence, 141 publications.
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Sample genotype (not yours): A/A
Altered Drug Metabolism and Moderately Higher Cancer Risk
Slower clearance of certain medications may increase the risk of side effects and toxicity. There is also a moderately elevated risk for developing specific types of cancers.
What this genotype means: Slower clearance of medications like methotrexate and tacrolimus; Higher risk of side effects from chemotherapy; Moderately increased risk for certain cancers.
Sample genotype (not yours): A/G
Slightly Altered Drug Metabolism
A single copy of the variant allele leads to a mild reduction in drug pump activity. Most medication responses and health risks remain close to typical levels.
What this genotype means: Intermediate drug pump activity; Generally typical response to most medications; Standard baseline risk for associated health conditions.
Sample genotype (not yours): G/G
Typical Drug Metabolism with Lower Cancer Risk
Standard cellular pump activity helps maintain typical drug clearance and a lower risk of certain cancers. However, there is a slightly higher risk of cannabis dependence.
What this genotype means: Standard drug clearance and typical medication response; Lower baseline risk for specific cancers; Slightly increased risk of cannabis dependence.
Gene function and biological role
Gene Function: The ABCB1 gene encodes P-glycoprotein, a vital cellular pump that acts as a protective barrier against toxins [1]. This pump is highly active in organs like the liver, kidneys, and intestines, where it flushes out foreign substances and medications [2]. By controlling how much of a drug enters or stays in cells, it directly influences medication levels in the bloodstream [1]. Variations in this gene can alter the pump's efficiency, leading to significant differences in drug side effects and therapeutic success [2].
Variant Impact: The rs1045642 variant is a synonymous change in the ABCB1 gene, meaning it does not alter the final amino acid sequence of the P-glycoprotein pump [2]. Despite being a silent mutation, it can significantly affect how the protein is folded and how fast it is produced [2]. This molecular shift alters the pump's ability to transport various medications across cell membranes [1]. As a result, this variant is one of the most widely studied genetic markers for predicting drug response and toxicity [1].
Key Insight: Even though this genetic change is silent and does not alter the protein sequence, it changes how the cellular pump folds, directly impacting how your body processes dozens of common medications.
Location: ABCB1. Chromosome 7 · 7q21.12 · 87.5 Mb
Estimated prevalence by population
Global 20.6%; European 28.2%; African 4.1%; East Asian 14.5%; South Asian 34.5%; Americas 18.6%; Ashkenazi 12.0%; Finnish 38.6%; Middle Eastern 22.4%; Amish 18.1%.
Estimated AA genotype frequency.
Global 44.5%; European 49.8%; African 32.3%; East Asian 47.2%; South Asian 48.5%; Americas 49.1%; Ashkenazi 45.3%; Finnish 47.1%; Middle Eastern 49.9%; Amish 48.9%.
Estimated AG genotype frequency.
Global 34.9%; European 22.0%; African 63.5%; East Asian 38.3%; South Asian 17.0%; Americas 32.3%; Ashkenazi 42.7%; Finnish 14.3%; Middle Eastern 27.8%; Amish 33.0%.
Estimated GG genotype frequency.
Showing effects for A/A genotype
Pharmacogenomics
Drug Metabolism Enzyme Activity
Medication Response. Evidence: 7/10. Source: PMID 10716719. Altered Response.
Anticoagulant & Blood Thinner Response
Clopidogrel Response. Evidence: 6/10. Source: PMID 19106083. Reduced Response.
Immunosuppressant & Biologic Response
Tacrolimus Response. Evidence: 6/10. Source: PMID 14747421. Slower Metabolism.
Cancer & Oncology
General Cancer Risk
General Cancer Risk. Evidence: 3/10. Source: PMID 24070710. Moderately Increased.
Neurology & Mental Health
Addiction & Reward
Cannabis Dependence. Evidence: 3/10. Source: PMID 24086514. Typical Risk.
Showing effects for A/G genotype
Medication Response. Evidence: 7/10. Source: PMID 10716719. Slower Metabolism.
Clopidogrel Response. Evidence: 6/10. Source: PMID 19106083. Slightly Reduced.
Tacrolimus Response. Evidence: 6/10. Source: PMID 14747421. Typical Response.
General Cancer Risk. Evidence: 3/10. Source: PMID 24070710. Typical Risk.
Showing effects for G/G genotype
Medication Response. Evidence: 7/10. Source: PMID 10716719. Typical Response.
Clopidogrel Response. Evidence: 6/10. Source: PMID 19106083. Typical Response.
General Cancer Risk. Evidence: 3/10. Source: PMID 24070710. Lower Risk.
Cannabis Dependence. Evidence: 3/10. Source: PMID 24086514. Increased Risk.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
Carrying two copies of the A allele is associated with reduced activity of the P-glycoprotein cellular pump [1]. This reduction can lead to slower metabolism and higher blood levels of several common medications, including methotrexate and tacrolimus [2]. Consequently, there is an increased likelihood of experiencing drug-induced side effects, such as liver damage or mucositis [2]. For blood thinners like clopidogrel, this altered transport can lead to a poorer therapeutic response and a higher risk of cardiovascular events [3]. Additionally, some studies suggest this genotype is linked to a moderately increased susceptibility to certain cancers, likely due to the accumulation of cellular toxins [4].
Slower clearance of medications like methotrexate and tacrolimus; Higher risk of side effects from chemotherapy; Moderately increased risk for certain cancers.
Sample genotype: AG (Heterozygous)
Having one copy of each allele typically results in intermediate P-glycoprotein pump activity [1]. Slower metabolism may occur for specific medications, but the clinical impact is generally mild compared to carrying two copies of the variant allele [2]. For instance, minor differences in the processing of immunosuppressants or blood thinners have been observed, though major complications are rare [2]. Overall health risks, including cancer susceptibility, do not show a strong or consistent deviation from the general population [3]. Most individuals with this genotype process standard drug doses without significant unexpected side effects [1].
Intermediate drug pump activity; Generally typical response to most medications; Standard baseline risk for associated health conditions.
Sample genotype: GG (Homozygous)
Two copies of the G allele represent the typical genetic baseline for P-glycoprotein pump function [1]. Efficient pump activity helps clear foreign toxins from cells, which is associated with a lower, baseline risk for several cancers [2]. Standard doses of medications like clopidogrel and tacrolimus are generally processed efficiently, leading to predictable therapeutic responses [3]. However, some behavioral genetics research has linked this genotype to an increased risk of developing cannabis dependence [4]. Aside from this specific behavioral association, overall drug transport and physiological health remain highly stable [1].
Standard drug clearance and typical medication response; Lower baseline risk for specific cancers; Slightly increased risk of cannabis dependence.
Variants with shared genetic architecture
rs2032582 · ABCB1 Gene · Chr 7 · Lung Cancer Risk
rs1128503 · ABCB1 Gene · Chr 7 · Medication Response
rs3213619 · ABCB1 Gene · Chr 7 · Chemotherapy Neuropathy Risk
A "silent" polymorphism in the MDR1 gene changes substrate specificity.
Genetic determinants of response to clopidogrel and cardiovascular events.
Association between MDR1 C3435T polymorphism and risk of breast cancer.
Content updated August 2026.
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