CYP2B6 rs61748181: What Your Genotype Means
The rs61748181 variant is a genetic alteration in the CYP2B6 gene associated with reduced enzymatic activity. This variant may impact how the body clears specific medications, such as efavirenz and methadone, particularly in individuals of African ancestry.
What each genotype means
Normal enzymatic activity
This genotype represents the most common form of the gene and is typically associated with normal CYP2B6 enzyme activity. You likely process medications metabolized by this enzyme, such as efavirenz or methadone, at an expected rate. Always discuss your medication dosing and any side effects with your clinician or pharmacist, as other factors may influence how your body handles specific drugs.
Carried by the vast majority of individuals globally, especially in non-African populations where the variant allele is extremely rare.
Reduced enzyme activity
Carrying one copy of the variant allele, which is associated with the CYP2B6*18 haplotype, may result in decreased CYP2B6 enzyme activity. This reduced function may lead to altered processing of certain medications, such as efavirenz, which can affect their clinical effectiveness or side-effect profile. Please consult with your pharmacist or physician to review how this might specifically impact your current or future medication management.
Observed primarily in populations of African ancestry, where the minor allele frequency is approximately 0.05 to 0.08.
Profound enzyme deficiency
This genotype is associated with the CYP2B6*18 allele, which has been shown to cause a profound deficiency in CYP2B6 enzymatic activity. Individuals with this genotype may have significantly impaired clearance of drugs like efavirenz or methadone, which may increase the risk of adverse effects or altered drug levels. It is important to discuss this specific genetic result with your healthcare provider or a clinical pharmacist before starting any new medications metabolized by this pathway.
Rare overall and primarily identified in individuals of African ancestry; it is essentially absent in most other global populations.
What is rs61748181 and Where Does it Sit?
The variant rs61748181 is a single nucleotide polymorphism (SNP) situated within the CYP2B6 gene, which provides instructions for making an enzyme essential for drug metabolism. In technical terms, this variant represents a missense mutation where a specific nucleotide change results in an amino acid substitution in the resulting protein. Specifically, this variant is the defining mutation for the CYP2B6*18 allele, a designation used by researchers to track functional changes in the enzyme. Because this change occurs in the DNA sequence that codes for the enzyme, it can alter the protein's shape or stability, potentially rendering it less effective at its job. When we talk about genetic variants, we are simply identifying these slight spelling differences in the human genome that occur naturally across different populations. Understanding where these variants sit—and how they change the code—is the first step in pharmacogenomics, the study of how genes influence drug response.
The Role of the CYP2B6 Gene
The CYP2B6 gene belongs to the cytochrome P450 superfamily, a large group of enzymes primarily located in the liver that are responsible for breaking down, or metabolizing, a vast array of substances, including endogenous compounds and exogenous drugs. Think of CYP2B6 as a molecular processing plant; its job is to modify chemicals so they can be easily cleared from the body. When the enzyme functions normally, drugs are processed at a predictable rate, maintaining therapeutic levels in the bloodstream. However, when a variant like rs61748181 causes profound enzymatic deficiency, the processing plant may slow down significantly or stop working efficiently. Consequently, medications that rely on this enzyme for clearance may linger in the system longer than intended. This can increase the concentration of the drug in the blood, which might heighten the risk of side effects or toxicity if the dose is not adjusted to account for the slower metabolism.
Research Associations and Evidence Strength
The evidence linking rs61748181 to altered drug metabolism is currently categorized as limited but significant in specific research contexts. Clinical studies have investigated this variant primarily in the context of efavirenz, an antiretroviral medication used to treat HIV, and methadone, used in opioid agonist therapy. Research suggests that individuals carrying this variant may experience impaired clearance of these substances. Because the enzyme is less active, patients with this genotype might reach higher drug concentrations in their plasma, which has been associated with an increased likelihood of central nervous system side effects. However, it is important to note that limited evidence means that large-scale, prospective clinical trials are still needed to fully standardize how this variant should be used in routine clinical decision-making. Researchers continue to study these associations to determine how much the dosage needs to be modified, if at all, to ensure both safety and therapeutic efficacy for patients.
Managing Your Genetic Information
If you discover you carry the rs61748181 variant, it is essential to keep this information in the proper context. Genetic testing is a tool for understanding biological predispositions, but it is not a diagnosis. Having this variant does not mean you will definitely experience side effects from medications, nor does it mean you should ever stop or change your medication regimen on your own. Medications are complex, and many factors—including weight, kidney function, other health conditions, and drug-drug interactions—influence how they work. If you have concerns about your genetic results and your medications, the best course of action is to schedule a consultation with your clinician or a specialized clinical pharmacist. They can review your complete medical history and determine if your genetic profile warrants a dose adjustment or a different therapeutic strategy. Your physician is the only person qualified to interpret these results and manage your care safely.
How common is this variant?
The minor allele frequency for rs61748181 is approximately 0.05 to 0.08 in African populations, while it is very rare or absent in other global populations.
Frequently asked questions
Does having the rs61748181 variant mean I cannot take certain drugs?
No, it does not mean you cannot take these medications. It simply means your body may process them differently, which might require your doctor to adjust your dosage to ensure the drug remains at a safe and effective level.
Should I stop taking my medication if I have this variant?
Absolutely not. You should never stop or change your prescription medication without talking to your doctor, as doing so can be dangerous. Your healthcare provider will weigh the benefits and risks of your treatment based on your entire health profile.
How do I get tested for this variant?
Genetic testing for pharmacogenomic markers is usually ordered by a physician or specialist if they suspect a patient is not responding well to a specific drug. Consult your doctor if you are interested in testing or have concerns about how your medications are working.
Why is this variant mostly found in African populations?
Genetic variants often arise and persist in specific populations due to the history and migration patterns of human groups. This variant is a known marker in certain African populations but is not common elsewhere in the world.
Sources & further reading
Educational information only, last refreshed 9/25/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs61748181?
Upload a raw DNA file from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA and see this variant — plus thousands more — interpreted in your full report.
Get my report — $29Related variants in CYP2B6
Defines the non-functional CYP2B6*18 allele (c.983T>C; p.Ile328Thr) leading to impaired metabolism of efavirenz.
Core coding variant c.1459C>T (p.Arg487Cys) defining CYP2B6*5, associated with reduced clearance of substrates.
Key variant defining the CYP2B6*6 reduced-function allele influencing efavirenz, methadone, and bupropion clearance.
A coding variant that defines the decreased-function CYP2B6*4 allele, influencing plasma concentrations of efavirenz, methadone, and bupropion.
Missense alteration defining the nonfunctional CYP2B6*18 allele common in African populations that slows clearance of efavirenz.
Encodes CYP2B6 c.1459C>T (p.Arg487Cys) defining the CYP2B6*5 allele, associated with reduced clearance of efavirenz and other substrates.