CYP2D6 rs1065852: What Your Genotype Means
The rs1065852 variant is a common genetic change located within the CYP2D6 gene, which provides instructions for an enzyme responsible for metabolizing many medications. This variant is associated with reduced enzyme activity, which can influence how an individual processes drugs such as antidepressants and antipsychotics.
What each genotype means
Normal enzyme activity
This genotype represents the wild-type or normal version of the CYP2D6 enzyme. Research suggests this version of the protein typically maintains standard metabolic clearance rates for medications processed by this pathway. Please discuss any medication dosing or concerns with your clinician or pharmacist.
This is the most common genotype in many populations, particularly among individuals of European ancestry.
Intermediate enzyme activity
Carrying one copy of the T allele may result in reduced intrinsic clearance of certain drugs compared to the C/C genotype. This variant is often associated with the CYP2D6*10 allele, which can lead to thermal instability of the enzyme. Please consult your healthcare provider or pharmacist regarding how this may influence your response to specific medications.
This genotype is frequently observed in global populations and is notably common in East Asian ancestries.
Reduced enzyme activity
This genotype is associated with lower metabolic activity for various drugs, as the T allele can lead to reduced protein stability and clearance. Because this variant is involved in the metabolism of many antidepressants and antipsychotics, your body may process these medications differently than expected. Always discuss your genetic profile and medication management with your prescribing clinician or pharmacist.
This genotype is more prevalent in East Asian populations compared to European populations, where it is less common.
Understanding the rs1065852 Variant
The rs1065852 variant, often referred to as c.100C>T or P34S, is a single nucleotide polymorphism (SNP) located on chromosome 22. In this specific location, the DNA sequence can contain either a cytosine (C) or a thymine (T). This change results in an amino acid substitution where proline is replaced by serine at position 34 of the CYP2D6 protein. Because this SNP is a component of several different star alleles—most notably the CYP2D6*10 allele—it is frequently studied in the context of pharmacogenomics. It is important to note that because this SNP appears in multiple genetic backgrounds, testing for rs1065852 alone does not provide a complete picture of an individual's total CYP2D6 enzyme function, as other structural variations and gene copies also play significant roles.
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 and is responsible for the metabolism of approximately 20% to 25% of all clinically used drugs. These include a wide range of therapeutic agents, such as antidepressants, antipsychotics, beta-blockers, and certain pain medications like codeine. Because the CYP2D6 gene is highly polymorphic, individuals can have different versions of the gene that result in enzyme activity levels ranging from completely absent to significantly increased. When an individual carries variants that reduce the efficiency of this enzyme, they may process these medications more slowly than others, potentially leading to higher drug concentrations in the blood and an increased risk of side effects or altered therapeutic responses.
Research and Clinical Associations
Scientific research has consistently associated the rs1065852 (T) allele with reduced enzymatic activity. Studies suggest that the protein produced by this variant may be less stable or have lower intrinsic clearance rates compared to the wild-type protein. This has been observed in clinical contexts where patients with the (T) allele show differences in how they respond to specific treatments, such as tamoxifen in breast cancer therapy or various psychiatric medications. However, the evidence strength for this specific SNP as a standalone predictor is considered moderate. Because CYP2D6 function is determined by the combination of all inherited alleles, including gene deletions or duplications, clinical guidelines often emphasize looking at the full genotype rather than a single SNP. Researchers continue to investigate how these genetic differences contribute to inter-individual variability in drug efficacy and safety.
What You Can Do With This Information
Genetic information regarding CYP2D6 can be a valuable tool for understanding your body's unique metabolic profile, but it should never be used to make independent medical decisions. If you have received results indicating you carry the rs1065852 variant, it is essential to discuss these findings with your healthcare provider or a clinical pharmacist. They can interpret your results in the context of your overall genetic profile and current medication regimen. Never stop, start, or change the dosage of any prescribed medication based on genetic test results without professional medical guidance. Your clinician can determine if a dosage adjustment or an alternative medication is appropriate based on your specific genotype and clinical needs. Pharmacogenomic testing is intended to support, not replace, the clinical judgment of your healthcare team.
How common is this variant?
The rs1065852 (T) allele is common in Asian populations, with frequencies ranging from 9% to 44%, while it is significantly less common in European and other populations.
Frequently asked questions
Does having the rs1065852 variant mean I cannot take certain medications?
Not necessarily. Having this variant may mean your body processes certain drugs differently, which might require your doctor to adjust your dose or choose a different medication. It does not mean you are allergic to or prohibited from taking these drugs.
Is rs1065852 the only variant that affects CYP2D6?
No, the CYP2D6 gene is highly complex and contains many different variants, including gene deletions and duplications. Testing for only one SNP like rs1065852 does not provide a complete assessment of your total CYP2D6 enzyme activity.
Should I get tested for this variant before starting a new medication?
Pharmacogenomic testing is not required for every medication. You should discuss with your doctor whether testing is relevant for the specific drug you are being prescribed and if it would help guide your treatment plan.
Where can I find more information about my specific CYP2D6 genotype?
You should consult with your prescribing physician or a clinical pharmacist. They can interpret your genetic report in the context of your medical history and provide guidance on how it might affect your treatment.
Sources & further reading
Educational information only, last refreshed 10/7/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Get my report — $29Related variants in CYP2D6
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.