CYP2D6 rs3892039: What Your Genotype Means
The rs3892039 variant is a well-studied single nucleotide polymorphism located in the CYP2D6 gene that disrupts normal RNA splicing. It is the defining variant for the widely documented CYP2D6*4 no-function allele, which leads to absent enzyme activity. Carrying this variant is statistically associated with impaired metabolism of dozens of clinically prescribed medications, including certain antidepressants, codeine, and tamoxifen.
What each genotype means
| Genotype | What the research suggests | Reading |
|---|---|---|
| CC | Carrying two copies of the C allele (equivalent to G/G on the opposite genomic strand) indicates the absence of the rs3892039-defined *4 non-functional allele. When paired with standard alleles, this genotype is typically consistent with normal CYP2D6 enzymatic activity. However, overall drug metabolism still depends on whether other loss-of-function variants or copy number changes are present in the gene. | Favorable |
| CT | Carrying one copy of the variant allele (equivalent to G/A on the opposite genomic strand) reflects heterozygosity for the non-functional CYP2D6*4 allele. Individuals with this genotype typically display intermediate metabolizer capacity if the other allele has normal function, though actual activity depends on the paired star allele. Drug clearance or prodrug activation may be slower compared to individuals with two fully functional alleles. | Informational |
| TT | Carrying two copies of the variant allele (equivalent to A/A on the opposite genomic strand) indicates homozygosity for the CYP2D6*4 non-functional allele. This genotype is strongly associated with a poor metabolizer phenotype characterized by absent CYP2D6 enzyme activity. Individuals with this profile face an increased likelihood of diminished therapeutic response to prodrugs or elevated toxicity risks from medications cleared by CYP2D6. | Higher attention |
What Is rs3892039 and Where Does It Sit?
The single nucleotide polymorphism rs3892039 is located on chromosome 22 within the cytochrome P450 family 2 subfamily D member 6 (CYP2D6) gene. In dbSNP and pharmacogenetic nomenclature, this variant represents a single base change—classically documented as a G to A transition at a critical splice acceptor site (often designated as c.506-1G>A or 1846G>A). Because it disrupts normal RNA splicing, the resulting messenger RNA produces a non-functional, truncated protein that entirely lacks enzymatic capability. In pharmacogenetics, this specific single nucleotide change is the hallmark defining lesion of the CYP2D6*4 haplotype, one of the most common non-functional star alleles identified across clinical medicine.
The Role of CYP2D6 in Drug Metabolism
The CYP2D6 enzyme is expressed primarily in the liver and belongs to the cytochrome P450 superfamily, which handles the breakdown and clearance of numerous compounds. Despite representing a modest percentage of total liver CYP enzymes, CYP2D6 is responsible for metabolizing approximately 20% of commonly prescribed therapeutic drugs across cardiology, psychiatry, oncology, and pain management. The enzyme either deactivates active medications to prepare them for excretion or converts inactive prodrugs into their therapeutic active metabolites. Because of its outsized pharmacological role, any loss-of-function variation within CYP2D6 significantly alters how long certain compounds remain in circulation or how efficiently prodrugs are activated.
Clinical Evidence and Drug Associations
Substantial clinical research evaluated by bodies such as the Clinical Pharmacogenetics Implementation Consortium (CPIC) and PharmGKB associates the *4 allele with altered patient drug responses. For prodrugs requiring CYP2D6 bioactivation—such as the pain reliever codeine converting to morphine, or tamoxifen converting to endoxifen—reduced or absent enzyme activity leads to significantly diminished clinical efficacy. Conversely, for active drugs that rely on CYP2D6 for metabolic clearance—such as select tricyclic antidepressants and selective serotonin reuptake inhibitors—reduced function can cause elevated drug plasma concentrations and increased risk of adverse side effects. While the catalog lists evidence strength for isolated single-variant tags as limited, the underlying biological consequence of the *4 haplotype itself is robustly documented across clinical guidelines.
Population Distribution and Ancestral Patterns
The frequency of the rs3892039 variant exhibits substantial geographic and ancestral variation across global populations. In individuals of European ancestry, the minor allele frequency typically ranges between 15% and 20%, making the *4 allele the most prevalent non-functional CYP2D6 variant in this group. In contrast, the variant is markedly less frequent in East Asian populations, often observed at frequencies below 2%, where other decreased-function variants like CYP2D6*10 predominate instead. African and Admixed American populations generally display intermediate allele frequencies. These ancestral disparities highlight why clinical pharmacogenetic screening panels genotype multiple distinct variants across diverse patient backgrounds rather than relying on a single marker.
Understanding What You Can and Cannot Do
A consumer genetic test identifying rs3892039 provides informative statistical data regarding inherited drug metabolism potential, but it is not a medical diagnosis. A single variant does not capture the full complexity of the CYP2D6 locus, which can include gene duplications, hybrid genes, or other non-functional star alleles on the opposite chromosome. Most importantly, genetic testing results should never be used to initiate, stop, or adjust prescription medication dosages independently. Phenotype expression is also modulated by co-prescribed medications that act as enzyme inhibitors or inducers. Always discuss your personal genotyping results with a qualified healthcare professional, clinician, or pharmacogenomics pharmacist before taking action.
How common is this variant?
The rs3892039 variant occurs at a minor allele frequency of approximately 15% to 20% in European populations, but it is rare in East Asian ancestries, where it is observed at rates under 2%.
Frequently asked questions
What does rs3892039 tell me about my medications?
This variant identifies whether you carry the non-functional CYP2D6*4 allele, which affects how rapidly your liver metabolizes certain medications. Depending on whether you carry zero, one, or two copies, your body may process medications like codeine, tamoxifen, and select antidepressants either normally, moderately, or poorly.
Does having the rs3892039 variant mean my medication will not work?
Not necessarily. For prodrugs that require CYP2D6 to become active (such as codeine), impaired metabolism may lead to reduced pain relief. However, for medications deactivated by CYP2D6, lower activity can actually cause higher blood concentrations, requiring careful clinical evaluation.
Should I change my medication dosage if I carry this variant?
No, you should never alter your medication dosage or stop treatment based on a genetic test result alone. Any changes must be discussed with your prescribing physician or a clinical pharmacist, who will evaluate your complete medical history and full CYP2D6 diplotype.
Can diet or lifestyle change how CYP2D6 works?
While diet and lifestyle support overall liver health, they cannot change the genetic structure or innate protein sequence of your CYP2D6 enzyme. However, certain foods and medications can temporarily inhibit or compete with CYP2D6, altering how effectively it clears other drugs.
Sources & further reading
Educational information only, last refreshed 9/9/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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