CYP2D6 rs28371706: What Your Genotype Means
The rs28371706 variant is a specific genetic change located within the CYP2D6 gene, which provides instructions for an enzyme responsible for processing many common medications. This variant is associated with altered enzyme activity, which can influence how an individual metabolizes drugs such as certain antidepressants and painkillers.
What each genotype means
Normal enzyme activity
This genotype is typically associated with normal CYP2D6 enzyme function, often referred to as the *1/*1 or wild-type status. Because this enzyme processes many antidepressants and painkillers, individuals with this profile generally metabolize these medications at expected rates. Please discuss your medication options and any concerns about dosing with your clinician or pharmacist.
This is the most common genotype observed across most global populations.
Reduced enzyme activity
This genotype includes the T allele, which is associated with reduced CYP2D6 enzyme activity, often linked to star alleles like *17 or *40. You may metabolize certain antidepressants and painkillers more slowly than individuals with the C/C genotype, which could influence how these drugs work for you. Please discuss your medication history and potential dosing adjustments with your clinician or pharmacist.
This genotype is found in approximately 10% of European populations, though frequencies vary significantly by ancestry.
Significantly reduced enzyme activity
This genotype indicates that both copies of your CYP2D6 gene carry the T allele, which is associated with reduced or no-function enzyme activity. You may be at a higher likelihood of altered drug response for medications processed by this enzyme, such as certain antidepressants or painkillers. Please consult with your clinician or pharmacist to review your treatment plan and ensure appropriate dosing.
This genotype is relatively rare in most populations, with specific prevalence depending on regional ancestry.
Understanding the rs28371706 Variant
The rs28371706 variant, also referred to in scientific literature as 1023C>T or T107I, is a single nucleotide polymorphism (SNP) situated on chromosome 22 within the CYP2D6 gene. This gene is highly polymorphic, meaning it contains many natural variations that differ between individuals. The rs28371706 variant specifically involves a change in the DNA sequence where a cytosine (C) is replaced by a thymine (T). This change is not an isolated marker; rather, it is a component of several defined CYP2D6 star alleles, including *17, *40, *58, and *64. Because these star alleles are associated with different levels of enzymatic function, identifying the presence of the T allele at this position is a key step in understanding an individual's potential metabolic profile for drugs processed by this enzyme.
The Role of the CYP2D6 Gene
The CYP2D6 gene encodes the cytochrome P450 2D6 enzyme, which is primarily expressed in the liver. This enzyme is a critical component of the body's detoxification system, responsible for the metabolism or bioactivation of approximately 20% to 25% of all clinically used medications. This includes a wide array of therapeutic agents such as antidepressants, neuroleptics, beta-blockers, and pain medications like codeine. Because the CYP2D6 gene is so complex and variable, the amount of functional enzyme produced can differ significantly from person to person. These differences result in a spectrum of metabolic activity, ranging from individuals who are 'poor metabolizers'—who process drugs very slowly—to 'ultrarapid metabolizers'—who process drugs much faster than average. Understanding these variations is essential for predicting how a patient might respond to standard drug dosages.
Research and Clinical Associations
Scientific research has established a strong link between CYP2D6 genetic variations and interindividual differences in drug response. The rs28371706 (T) allele is specifically recognized for its association with decreased or non-functioning enzyme activity. When an individual carries these variants, the liver may struggle to break down or activate medications at the expected rate, which can lead to either an accumulation of the drug in the system or a failure to produce the active form of the medication. While the evidence linking this specific SNP to altered drug metabolism is well-documented in pharmacogenetic studies, it is important to note that clinical outcomes can be influenced by many factors, including other genetic variants, drug-drug interactions, and environmental influences. Consequently, the predictive power of a single SNP is often viewed as one piece of a larger clinical puzzle.
What You Can Do With This Information
If you have received information about your rs28371706 genotype, it is important to interpret it within the context of your overall health and current medication regimen. This genetic information is intended for educational purposes and should never be used to self-diagnose or alter your medical treatment. Because drug metabolism is complex, a single variant does not provide a complete picture of how your body will respond to a specific drug. If you are concerned about how your genetics might affect your response to a medication, the most appropriate step is to consult with your physician or a clinical pharmacist. They can review your genetic results alongside your medical history and current prescriptions to determine if a dosage adjustment or an alternative medication might be appropriate for your specific needs.
How common is this variant?
The rs28371706 variant is found in approximately 10% of European populations, though frequencies vary significantly across different global ancestries.
Frequently asked questions
Does having the T allele mean I cannot take certain medications?
Not necessarily. Having the T allele suggests your body may process certain drugs differently, but it does not mean you cannot take them. Your doctor may simply need to adjust the dosage or choose a different medication to ensure it is safe and effective for you.
Is rs28371706 the only variant that affects CYP2D6?
No, the CYP2D6 gene is highly complex and contains many different variants. A comprehensive assessment of your metabolic status usually requires looking at multiple variants and star alleles, not just this single SNP.
Can I use this information to change my medication dosage?
No. You should never change your medication dosage or stop taking a prescribed drug based on genetic test results without consulting your healthcare provider. Only a clinician can safely determine if a change in your treatment plan is necessary.
Where can I get a professional interpretation of my genetic results?
You should discuss your genetic reports with your primary care physician, a specialist, or a clinical pharmacist. These professionals are trained to interpret pharmacogenetic data in the context of your specific health needs.
Sources & further reading
Educational information only, last refreshed 10/8/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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This variant is a key marker for the CYP2D6*10 allele, which results in reduced enzymatic activity and altered metabolism of various psychiatric and analgesic medications.
This variant defines the CYP2D6*4 non-functional allele, which causes impaired metabolism of numerous clinically prescribed medications including antidepressants, tamoxifen, and codeine.
Defines the CYP2D6*17 allele (p.Thr107Ile), which exhibits reduced enzyme activity towards substrates like codeine and certain antidepressants.
Defines the CYP2D6*29 variant (p.Val338Met) conferring decreased metabolic capacity, primarily observed in populations of African descent.
Promoter variant defining the CYP2D6*41 allele, associated with reduced enzyme expression and decreased metabolic capacity for various drugs.
Defines the CYP2D6*6 deletion variant (1707delT) leading to a premature stop codon and loss of enzyme function.