What you carry at this position in your DNA and what research says about it.
Medication Response: 5/10 evidence, 13 publications.
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Sample genotype (not yours): C/C
Typical Drug Metabolism
Standard enzyme activity supports typical processing of several common medications. This includes normal clearance rates for chemotherapy drugs, methadone, and bupropion.
What this genotype means: Standard chemotherapy outcomes; Typical methadone clearance.
Sample genotype (not yours): C/T
Altered Chemotherapy and Smoking Cessation Response
One copy of the variant allele is linked to a higher success rate when using bupropion to quit smoking. However, it may also increase the risk of relapse following certain chemotherapy treatments.
What this genotype means: Increased likelihood of smoking cessation success; Elevated risk of chemotherapy relapse.
Sample genotype (not yours): T/T
Slower Drug Metabolism and Chemotherapy Risks
Two copies of the variant allele significantly slow down the clearance of certain medications. This increases the risk of transplant complications and alters response to smoking cessation therapies.
What this genotype means: Slower methadone clearance; Increased risk of post-transplant complications.
Gene function and biological role
Gene Function: The CYP2B6 gene encodes a member of the cytochrome P450 superfamily of enzymes, which are primarily responsible for metabolizing clinical drugs and foreign compounds in the liver [1]. This specific enzyme plays a critical role in processing diverse therapeutics, including the chemotherapy prodrug cyclophosphamide, the antidepressant bupropion, and the opioid agonist methadone [1] [2]. Genetic variations in this gene can significantly alter enzyme expression and catalytic activity, leading to wide differences in drug clearance and therapeutic outcomes [2]. Some variants reduce the functional enzyme levels in liver tissue, while others can subtly increase specific metabolic activity [2] [3]. Understanding these genetic differences helps explain why individuals respond differently to identical medication regimens [3].
Variant Impact: The rs3211371 variant is a missense mutation in the CYP2B6 gene that results in an amino acid substitution of cysteine for arginine at position 487 of the protein [4]. This molecular change defines the CYP2B6*5 allele, which is associated with altered enzyme expression and metabolic capacity [4] [2]. In the liver, this variant can lead to decreased overall expression of the CYP2B6 enzyme, although this is sometimes partially compensated by changes in specific catalytic activity [2]. Consequently, individuals carrying this variant may exhibit altered clearance rates for several clinically important medications [2] [5]. These pharmacokinetic differences can impact the efficacy and safety profiles of treatments ranging from cancer chemotherapy to smoking cessation therapies [5] [6].
Key Insight: This variant can simultaneously increase the success rate of quitting smoking with bupropion while raising the risk of relapse during chemotherapy.
Location: CYP2B6. Chromosome 19 · 19q13.2 · 41.0 Mb
Estimated prevalence by population
Global 84.3%; European 77.1%; African 94.8%; East Asian 99.0%; South Asian 85.9%; Americas 89.5%; Ashkenazi 79.1%; Finnish 77.2%; Middle Eastern 86.9%; Amish 67.7%.
Estimated CC genotype frequency.
Global 14.8%; European 21.5%; African 5.1%; East Asian 1.0%; South Asian 13.6%; Americas 10.2%; Ashkenazi 19.6%; Finnish 21.3%; Middle Eastern 12.7%; Amish 29.1%.
Estimated CT genotype frequency.
Global 0.9%; European 1.5%; African 0.1%; East Asian < 0.1%; South Asian 0.5%; Americas 0.3%; Ashkenazi 1.2%; Finnish 1.5%; Middle Eastern 0.5%; Amish 3.1%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Pharmacogenomics
Chemotherapy Response
Chemotherapy Response. Evidence: 5/10. Source: PMID 25677220. Typical Response.
Pain Medication Response
Methadone Metabolism. Evidence: 5/10. Source: PMID 28184434. Typical Metabolism.
Neurology & Mental Health
Addiction & Reward
Smoking Cessation. Evidence: 5/10. Source: PMID 12439223. Typical Success.
Showing effects for C/T genotype
Chemotherapy Response. Evidence: 5/10. Source: PMID 25677220. Increased Relapse Risk.
Smoking Cessation. Evidence: 5/10. Source: PMID 12439223. Higher Success Rate.
Showing effects for T/T genotype
Chemotherapy Response. Evidence: 5/10. Source: PMID 25677220. Higher GVHD Risk.
Methadone Metabolism. Evidence: 5/10. Source: PMID 28184434. Slower Metabolism.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Two copies of the reference allele result in typical CYP2B6 enzyme expression and activity levels in the liver [1]. Standard metabolic processing helps maintain expected therapeutic levels of medications like cyclophosphamide, minimizing the risk of premature treatment relapse [1] [2]. It also ensures normal clearance of methadone, reducing the likelihood of toxic accumulation or related adverse events [3]. While this typical activity profile does not provide the elevated smoking cessation success rates seen with variant carriers, it represents the baseline standard of care [4]. Clinical guidelines and standard dosing protocols are generally optimized for individuals with this typical metabolizer profile [1] [3].
Standard chemotherapy outcomes; Typical methadone clearance.
Sample genotype: CT (Heterozygous)
Presence of a single variant allele alters the liver's capacity to metabolize several common therapeutic agents [1]. Clinical studies indicate that this genotype is associated with an increased likelihood of successful smoking cessation when using bupropion [2]. Conversely, the same metabolic shift is linked to a higher risk of disease recurrence and reduced survival following cyclophosphamide-containing chemotherapy regimens [1] [3]. This dual effect highlights how a single genetic change can be beneficial for one treatment while introducing risks for another [2] [3]. Healthcare providers can use this genetic profile to better evaluate the balance of risks and benefits for specific drug therapies [1] [2].
Increased likelihood of smoking cessation success; Elevated risk of chemotherapy relapse.
Sample genotype: TT (Homozygous)
Two copies of the variant allele lead to a pronounced reduction in the clearance of specific medications metabolized by CYP2B6 [1]. This slower metabolism is associated with a significantly increased risk of complications, such as graft-versus-host disease, after cyclophosphamide-containing conditioning regimens [2]. It also leads to slower clearance of methadone, which can cause the drug to accumulate in the body and increase the risk of adverse effects [1]. On the positive side, this genotype is linked to a higher likelihood of successful smoking cessation when using bupropion [3]. These diverse clinical impacts underscore the importance of personalized medication management for individuals with this genetic profile [1] [2].
Slower methadone clearance; Increased risk of post-transplant complications.
Variants with shared genetic architecture
rs28399499 · CYP2B6 Gene · Chr 19 · HIV Medication Sensitivity
rs3745274 · CYP2B6 Gene · Chr 19 · Medication Metabolism
rs2279343 · CYP2B6 Gene · Chr 19 · Drug Metabolism and Mastocytosis
Tell-Tale SNPs: The Role of CYP2B6 in Methadone Fatalities.
Pharmacogenetic investigation of smoking cessation treatment.
Content updated August 2026.
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