What you carry at this position in your DNA and what research says about it.
Drug Metabolism and Mastocytosis: 5/10 evidence, 21 publications.
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Sample genotype (not yours): A/A
Typical Mastocytosis Risk and Standard Drug Clearance
This genotype is associated with a baseline risk of mast cell disorders and typical processing of several common medications. It may also indicate a higher likelihood of success when using bupropion for smoking cessation.
What this genotype means: Typical risk of cutaneous mastocytosis; May respond less strongly to methadone if prescribed; Higher likelihood of smoking cessation success with bupropion.
Sample genotype (not yours): A/G
Lower Mastocytosis Risk and Altered Drug Sensitivity
Carrying one copy of the variant G allele provides moderate protection against cutaneous mastocytosis while slightly altering how the liver processes certain medications.
What this genotype means: Reduced risk of cutaneous mastocytosis; Altered clearance of anesthetics and chemotherapy drugs; Typical methadone response.
Sample genotype (not yours): G/G
Lowest Mastocytosis Risk and Slower Drug Metabolism
Carrying two copies of the variant G allele offers the strongest protection against cutaneous mastocytosis but significantly slows the clearance of medications like efavirenz.
What this genotype means: Lowest risk of cutaneous mastocytosis; Slower metabolism of efavirenz, with greater sensitivity to it; Altered clearance of propofol and cyclophosphamide.
Gene function and biological role
Gene Function: The CYP2B6 gene encodes a key member of the cytochrome P450 enzyme family, which is primarily active in the liver and responsible for processing various clinical medications [1]. This enzyme plays a vital role in metabolizing therapeutic drugs such as the HIV medication efavirenz, the opioid addiction treatment methadone, and the antidepressant bupropion [1]. Genetic variations within this gene can significantly alter enzyme expression and activity, leading to wide differences in how quickly individuals clear these substances from their bodies [2]. Beyond drug processing, research suggests that CYP2B6 expression levels may also influence susceptibility to certain rare immune-related disorders [3].
Variant Impact: The rs2279343 variant is a missense mutation in the CYP2B6 gene that causes an amino acid substitution from lysine to arginine at position 262 of the protein, commonly referred to as p.Lys262Arg. This specific genetic change alters the structural stability and catalytic activity of the CYP2B6 enzyme [1]. When present on its own, this variant defines the CYP2B6*4 star allele, which is generally associated with increased enzyme activity and faster drug clearance. However, it frequently co-occurs with other mutations to form the CYP2B6*6 allele, which paradoxically results in significantly reduced enzyme expression and slower drug metabolism [4]. Additionally, this genetic change has been linked to altered susceptibility to mast cell disorders [3].
Key Insight: While this genetic variant is famous for altering how the liver processes common medications, a genome-wide study revealed it also influences the risk of developing mastocytosis, a rare disorder characterized by the abnormal accumulation of mast cells in the skin.
Location: CYP2B6. Chromosome 19 · 19q13.2 · 41.0 Mb
Estimated prevalence by population
Global 50.2%; European 56.0%; African 41.4%; East Asian 53.2%; South Asian 37.7%; Americas 43.9%; Ashkenazi 46.6%; Finnish 60.2%; Middle Eastern 46.3%; Amish 76.9%.
Estimated AA genotype frequency.
Global 40.9%; European 37.7%; African 45.9%; East Asian 39.5%; South Asian 47.4%; Americas 44.7%; Ashkenazi 43.3%; Finnish 34.8%; Middle Eastern 43.5%; Amish 21.6%.
Estimated AG genotype frequency.
Global 8.9%; European 6.4%; African 12.7%; East Asian 7.3%; South Asian 14.9%; Americas 11.4%; Ashkenazi 10.0%; Finnish 5.0%; Middle Eastern 10.2%; Amish 1.5%.
Estimated GG genotype frequency.
Showing effects for A/A genotype
Immunity & Inflammation
Allergy & Hypersensitivity
Mastocytosis. Evidence: 5/10. Source: PMID 32752121. Typical Risk.
Pharmacogenomics
Antimicrobial & Antiviral Response
Efavirenz Response. Evidence: 7/10. Source: PMID 15194512. Typical Metabolism.
Pain Medication Response
Methadone Dosage. Evidence: 6/10. Source: PMID 21790905. Higher Tolerance.
Antidepressant & Psychiatric Drug Response
Bupropion Response. Evidence: 5/10. Source: PMID 26153084. Stronger Response.
Showing effects for A/G genotype
Mastocytosis. Evidence: 5/10. Source: PMID 32752121. Lower Risk.
Efavirenz Response. Evidence: 7/10. Source: PMID 15194512. Slightly Slower.
Methadone Dosage. Evidence: 6/10. Source: PMID 21790905. Typical Response.
Bupropion Response. Evidence: 5/10. Source: PMID 26153084. Typical Response.
Showing effects for G/G genotype
Mastocytosis. Evidence: 5/10. Source: PMID 32752121. Lowest Risk.
Efavirenz Response. Evidence: 7/10. Source: PMID 15194512. Slower Metabolism.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
Carrying two copies of the reference A allele means the CYP2B6 enzyme functions at a standard baseline level for most individuals. In the context of immune health, this genotype is associated with a typical risk of developing cutaneous mastocytosis, as it lacks the protective effect of the variant G allele [1]. Regarding medication response, individuals with this genotype who undergo methadone therapy for opioid addiction often respond less strongly to it [2]. Additionally, infants born to mothers with this genotype may experience more severe neonatal withdrawal symptoms if exposed to methadone during pregnancy [3]. On a positive note, clinical research indicates that this genotype is associated with a significantly better response and higher success rates when using bupropion as a smoking cessation aid [4].
Typical risk of cutaneous mastocytosis; May respond less strongly to methadone if prescribed; Higher likelihood of smoking cessation success with bupropion.
Sample genotype: AG (Heterozygous)
Having one copy of the variant G allele is associated with a reduced risk of developing cutaneous mastocytosis, a rare condition involving abnormal mast cell accumulation in the skin [1]. This genetic profile moderately influences the liver's ability to clear several therapeutic compounds. For instance, individuals with this genotype may experience altered clearance rates for the anesthetic propofol and the chemotherapy drug cyclophosphamide. In pediatric patients treated with cyclophosphamide for certain cancers, carrying this variant has been linked to improved overall survival outcomes, though it may also increase the risk of side effects like mouth ulcers [2]. Furthermore, this genotype is associated with a typical response to methadone therapy, generally showing greater sensitivity to it than those with the AA genotype [3].
Reduced risk of cutaneous mastocytosis; Altered clearance of anesthetics and chemotherapy drugs; Typical methadone response.
Sample genotype: GG (Homozygous)
Carrying two copies of the variant G allele is associated with the lowest risk of developing cutaneous mastocytosis, providing a strong protective benefit against this mast cell disorder [1]. However, this genotype also has pronounced effects on liver enzyme activity, particularly when the variant co-occurs with other mutations to form the slow-metabolizing CYP2B6*6 pathway [2]. Consequently, individuals with this genotype process the HIV medication efavirenz much more slowly, leading to higher drug concentrations in the blood [2]. Because of this slower clearance, clinical guidelines often suggest that lower doses of efavirenz may be highly effective while minimizing central nervous system side effects. Additionally, this genotype is linked to faster clearance of the anesthetic propofol and altered clinical outcomes during cyclophosphamide chemotherapy.
Lowest risk of cutaneous mastocytosis; Slower metabolism of efavirenz, with greater sensitivity to it; Altered clearance of propofol and cyclophosphamide.
Variants with shared genetic architecture
rs28399499 · CYP2B6 Gene · Chr 19 · HIV Medication Sensitivity
rs3745274 · CYP2B6 Gene · Chr 19 · Medication Metabolism
rs3211371 · CYP2B6 Gene · Chr 19 · Medication Response
Functional characterization of cytochrome P450 2B6 allelic variants.
CYP2B6 SNPs are associated with methadone dose required for effective treatment of opioid addiction.
CYP2B6 rs2279343 polymorphism is associated with smoking cessation success in bupropion therapy.
Content updated August 2026.
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