CYP2D6 rs104894300: What Your Genotype Means
The rs104894300 variant is a specific genetic marker located within the CYP2D6 gene, which plays a critical role in how the body processes many common medications. Variations in this gene are associated with differences in how quickly or slowly an individual metabolizes drugs, including certain antidepressants and antipsychotics.
What each genotype means
Normal enzyme activity
This genotype is typically associated with normal CYP2D6 enzyme function, often referred to as a normal metabolizer status. Because CYP2D6 is involved in processing many medications, including certain antidepressants and antipsychotics, your body may metabolize these drugs at an expected rate. Please discuss your medication options and potential dosing with your clinician or pharmacist, as other factors like drug-drug interactions can also influence how your body processes medicine.
This is a common genotype found across many global populations, though the specific frequency varies significantly by ancestry.
Possible reduced enzyme activity
This genotype includes one variant allele that may be associated with altered CYP2D6 enzyme activity compared to the standard reference. Research indicates that individuals with such variants may experience differences in how they metabolize specific psychiatric and pain medications. You should consult with your healthcare provider or pharmacist before starting new treatments to determine if your genotype warrants adjustments to medication selection or dosage.
This genotype is observed at varying frequencies worldwide, with specific variant alleles being more prevalent in certain East Asian and African populations.
Likely reduced enzyme activity
Carrying two copies of this variant may lead to reduced or altered CYP2D6 enzyme function, which can affect the metabolism of various common drugs. Clinical studies suggest that this status may influence the effectiveness or side-effect profile of medications like antidepressants or antipsychotics. It is important to share this information with your doctor or pharmacist so they can consider your genetic profile when managing your prescriptions.
This genotype is less common than the homozygous reference state but is found in diverse populations, with specific frequencies heavily dependent on your ancestral background.
Understanding the CYP2D6 Gene
The CYP2D6 gene provides instructions for making an enzyme that is part of the cytochrome P450 family. This enzyme is responsible for breaking down, or metabolizing, approximately 20% to 25% of all clinically used drugs. Because this enzyme is involved in the processing of such a wide array of medications—ranging from antidepressants and antipsychotics to pain relievers like codeine—the activity level of the CYP2D6 enzyme can significantly influence how a person responds to treatment. When the gene functions normally, the body clears these medications at a predictable rate. However, genetic variations can lead to reduced, absent, or even increased enzyme activity, which may change the concentration of a drug in the bloodstream and potentially affect both the efficacy and the safety profile of a prescribed therapy.
What is the rs104894300 Variant?
The rs104894300 variant is a specific polymorphism found within the sequence of the CYP2D6 gene. In the context of pharmacogenomics, researchers study such variants to understand how they correlate with different metabolic phenotypes. While some variants in CYP2D6 result in a complete loss of function, others may only partially reduce the enzyme's ability to process drugs. The evidence strength for many specific SNPs in this gene is considered moderate, as the clinical impact often depends on the combination of all inherited alleles, known as a diplotype. Because CYP2D6 is highly polymorphic, meaning it has many different variations, scientists often group these variants into 'star alleles' to better predict clinical outcomes. The rs104894300 variant is one of many markers used to identify these functional groups, helping clinicians understand why some patients might experience side effects or lack of response to standard medication doses.
Clinical Associations and Evidence
Research into CYP2D6 has established that genetic testing can provide valuable insights for personalized medicine, particularly in psychiatry. Studies have shown that individuals with certain genotypes may be classified as 'poor,' 'intermediate,' 'normal,' or 'ultra-rapid' metabolizers. For instance, those who are poor metabolizers may have higher levels of a drug in their system, increasing the risk of side effects, while ultra-rapid metabolizers might clear the drug too quickly for it to be effective. It is important to note that while associations between specific genotypes and drug responses have been observed in clinical studies, the evidence can be complex. Factors such as drug-drug interactions, age, and liver function also play significant roles. Consequently, pharmacogenomic data is intended to be used as one tool among many in a clinical setting to help guide, but not dictate, treatment decisions.
Navigating Your Genetic Information
If you have received information about your CYP2D6 genotype, it is essential to understand that this data does not provide a diagnosis or a definitive prediction of how you will react to every medication. Genetic testing for pharmacogenomics is a specialized field, and results should always be interpreted by a qualified healthcare professional, such as a doctor or a pharmacist. You should never change your medication dosage or stop taking a prescribed drug based on genetic test results without consulting your clinician. They can integrate your genetic profile with your medical history, current symptoms, and other medications you may be taking to determine the safest and most effective treatment plan. Pharmacogenomics is a rapidly evolving field, and clinical guidelines, such as those provided by the Clinical Pharmacogenetics Implementation Consortium (CPIC), are frequently updated as new research emerges.
How common is this variant?
The frequency of CYP2D6 variants is highly variable across different global populations and ethnic groups. Because of this diversity, the prevalence of specific genotypes like rs104894300 can differ significantly depending on an individual's ancestral background.
Frequently asked questions
Does my CYP2D6 genotype mean I cannot take certain medications?
Not necessarily. A specific genotype may suggest that you metabolize a drug differently, which might lead a doctor to adjust your dose or choose an alternative medication, but it rarely means a drug is strictly off-limits.
Can I use a home DNA test to determine my drug response?
While some consumer tests provide information on CYP2D6, these results should be confirmed by a clinical-grade test ordered by your healthcare provider. Always discuss these results with a professional before making any changes to your health regimen.
What is a 'poor metabolizer'?
A poor metabolizer is someone whose body processes certain drugs much more slowly than average due to genetic variations. This can lead to higher drug concentrations in the blood, potentially increasing the risk of side effects.
Are there other factors that affect how I process drugs?
Yes, many factors beyond genetics influence drug metabolism, including your age, liver and kidney function, diet, and other medications or supplements you may be taking.
Sources & further reading
Educational information only, last refreshed 10/3/2026. 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 non-functional CYP2D6*41 splice defect associated with intermediate metabolizer phenotype affecting codeine, tamoxifen, and SSRI metabolism.