What you carry at this position in your DNA and what research says about it.
Medication Response: 6/10 evidence, 80 publications.
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Sample genotype (not yours): A/A
Altered Drug Transport and Higher Sensitivity to Medication Side Effects
P-glycoprotein activity is altered, leading to slower clearance of certain medications and an increased risk of side effects. This can result in higher susceptibility to chemotherapy-induced nerve damage and reduced efficacy of some pain relievers. Close coordination with healthcare providers is helpful when starting new therapies.
What this genotype means: Higher risk of paclitaxel-induced neuropathy; Increased risk of methotrexate toxicity; Poorer response to fentanyl pain relief.
Sample genotype (not yours): A/G
Intermediate Drug Transport with Moderate Risk of Side Effects
A single copy of the altered allele results in intermediate P-glycoprotein transporter activity. This leads to moderate changes in drug clearance, slightly increasing the risk of chemotherapy side effects and affecting pain medication requirements. Monitoring drug levels can help optimize therapeutic outcomes.
What this genotype means: Moderate risk of chemotherapy-induced neuropathy; Altered response to methadone; Increased risk of immunosuppressant-related infection.
Sample genotype (not yours): G/G
Typical Drug Transport and Standard Medication Clearance
Standard P-glycoprotein transporter activity ensures typical clearance of many common medications. This profile is associated with a lower risk of chemotherapy-induced nerve damage and typical responses to pain relievers. However, certain drugs like immunosuppressants may still require careful monitoring.
What this genotype means: Typical risk of chemotherapy-induced neuropathy; Standard response to pain medications; Potential for faster clearance of immunosuppressants.
Gene function and biological role
Gene Function: The ABCB1 gene encodes P-glycoprotein, a vital ATP-dependent efflux pump located in cell membranes throughout the body [1]. This transporter acts as a protective barrier, pumping toxins and foreign substances out of cells in key organs like the brain, gut, kidneys, and liver [1]. Because many common medications are substrates for P-glycoprotein, variations in this gene can significantly alter how drugs are absorbed, distributed, and eliminated [2]. Consequently, ABCB1 is one of the most heavily studied pharmacogenomic genes, directly influencing the efficacy and safety of chemotherapy, immunosuppressants, and pain relievers [2].
Variant Impact: The rs1128503 variant is a synonymous change in exon 12 of the ABCB1 gene, often referred to as C1236T [2]. Although it does not change the resulting amino acid sequence of the P-glycoprotein transporter, it can influence translation kinetics and mRNA stability, ultimately altering protein folding and efflux activity [2]. This altered transport capability directly impacts how efficiently various medications are pumped out of target tissues [3]. As a result, this specific genetic marker is widely associated with clinical variability in drug response, chemotherapy-induced toxicities, and transplant outcomes [3].
Key Insight: Even though this genetic change does not alter the final protein sequence, it can change the speed of protein translation, which ultimately alters how your body processes dozens of common medications.
Location: ABCB1. Chromosome 7 · 7q21.12 · 87.6 Mb
Estimated prevalence by population
Global 16.1%; European 19.0%; African 3.7%; East Asian 40.3%; South Asian 35.8%; Americas 18.2%; Ashkenazi 13.4%; Finnish 23.5%; Middle Eastern 20.8%; Amish 11.0%.
Estimated AA genotype frequency.
Global 44.0%; European 49.2%; African 31.2%; East Asian 46.4%; South Asian 48.1%; Americas 48.9%; Ashkenazi 46.4%; Finnish 50.0%; Middle Eastern 49.6%; Amish 44.3%.
Estimated AG genotype frequency.
Global 39.9%; European 31.8%; African 65.0%; East Asian 13.3%; South Asian 16.1%; Americas 32.9%; Ashkenazi 40.2%; Finnish 26.5%; Middle Eastern 29.6%; Amish 44.7%.
Estimated GG genotype frequency.
Showing effects for A/A genotype
Pharmacogenomics
Chemotherapy Response
Chemotherapy Toxicity. Evidence: 6/10. Source: PMID 34280009. Higher Risk.
Pain Medication Response
Pain Relief Response. Evidence: 5/10. Source: PMID 22277678. Reduced Efficacy.
Immunosuppressant & Biologic Response
Transplant Safety. Evidence: 5/10. Source: PMID 26107754. Higher Infection Risk.
Cardiovascular Drug Response
Digoxin Safety. Evidence: 5/10. Source: PMID 26531821. Higher Risk.
Showing effects for A/G genotype
Pain Relief Response. Evidence: 5/10. Source: PMID 22277678. Slightly Reduced.
Digoxin Safety. Evidence: 5/10. Source: PMID 26531821. Typical Risk.
Showing effects for G/G genotype
Chemotherapy Toxicity. Evidence: 6/10. Source: PMID 34280009. Typical Risk.
Pain Relief Response. Evidence: 5/10. Source: PMID 22277678. Typical Response.
Transplant Safety. Evidence: 5/10. Source: PMID 26107754. Higher Rejection Risk.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
Slower clearance of several common drugs is a hallmark of this genetic profile, as the altered transporter function allows substances to accumulate in tissues [1]. When undergoing chemotherapy with paclitaxel, there is a significantly higher likelihood of developing peripheral neuropathy, characterized by pain and tingling in the hands and feet [2]. Similarly, treatment with methotrexate carries an elevated risk of severe mucositis and general drug toxicity [3]. Pain management can also be affected, with studies showing a poorer response to fentanyl and a reduced response to methadone during recovery therapies [4]. Immunosuppressive therapy with tacrolimus or cyclosporine is associated with a higher risk of infection due to altered drug levels [5]. Finally, there is an associated risk of adverse cardiovascular events when taking digoxin [6].
Higher risk of paclitaxel-induced neuropathy; Increased risk of methotrexate toxicity; Poorer response to fentanyl pain relief.
Sample genotype: AG (Heterozygous)
Transporter activity falls between the two homozygous profiles, creating a moderate shift in how various medications are processed [1]. During chemotherapy regimens involving paclitaxel, there remains an elevated risk of experiencing peripheral neuropathy and gastrointestinal side effects like nausea [2]. Methotrexate therapy also shows a higher likelihood of liver damage and mucositis due to altered drug clearance [3]. For pain management, intermediate transporter function may lead to a reduced response to methadone [4]. Additionally, patients receiving immunosuppressants like tacrolimus or cyclosporine face an increased risk of infection, and are often monitored closely [5]. These findings highlight the importance of personalized medicine approaches when prescribing P-glycoprotein substrates [1].
Moderate risk of chemotherapy-induced neuropathy; Altered response to methadone; Increased risk of immunosuppressant-related infection.
Sample genotype: GG (Homozygous)
Efficient efflux of foreign substances and medications from cells is maintained by the typical P-glycoprotein transporter activity associated with this profile [1]. Standard clearance rates help protect nerve tissues, resulting in a lower risk of paclitaxel-induced peripheral neuropathy compared to other genotypes [2]. Pain management therapies, including methadone and fentanyl, typically follow standard dosing guidelines with expected efficacy [3]. However, rapid clearance of certain medications can sometimes reduce their effectiveness. For instance, transplant patients taking tacrolimus or cyclosporine may experience faster metabolism of these drugs, which is linked to an increased risk of organ rejection [4]. Additionally, chemotherapy with cytarabine may show decreased survival rates and a higher risk of heart damage [5]. These variations underscore that even typical transporter activity has unique clinical implications depending on the specific drug used [1].
Typical risk of chemotherapy-induced neuropathy; Standard response to pain medications; Potential for faster clearance of immunosuppressants.
Variants with shared genetic architecture
rs1045642 · ABCB1 Gene · Chr 7 · Medication Response
rs2032582 · ABCB1 Gene · Chr 7 · Lung Cancer Risk
rs3213619 · ABCB1 Gene · Chr 7 · Chemotherapy Neuropathy Risk
ABCB1 gene variants, digoxin and risk of sudden cardiac death in a general population.
CYP2B6 SNPs are associated with methadone dose required for effective treatment of opioid addiction.
Content updated August 2026.
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