CYP2D6 rs113926168: What Your Genotype Means
The rs113926168 variant is a genetic change in the CYP2D6 gene that results in a non-functional enzyme. This variant defines the CYP2D6*6 allele, which is associated with impaired metabolism of various commonly prescribed medications.
What each genotype means
Normal enzyme activity
This genotype represents the presence of two functional copies of the CYP2D6 gene, often referred to as the wild-type or normal-function state. Individuals with this profile typically exhibit standard metabolic processing for drugs cleared by the CYP2D6 enzyme. Please discuss any medication dosing or potential drug interactions with your clinician or pharmacist.
This is the most common genotype observed across global populations.
Reduced enzyme activity
This genotype indicates that one copy of the gene carries the rs113926168 variant, which is associated with the non-functional CYP2D6*6 allele. Because the other copy is functional, your body may metabolize certain medications at a slower rate than average. Please consult your healthcare provider or pharmacist regarding how this may influence your response to specific CYP2D6 substrate drugs.
The minor allele is found at a frequency of approximately 0.01 in European populations and is considered rare in other ancestral groups.
Impaired enzyme activity
This genotype indicates that both copies of the gene carry the rs113926168 variant, which defines the non-functional CYP2D6*6 allele. This may lead to significantly impaired metabolism of drugs that rely on this enzyme for clearance, potentially increasing the risk of side effects or reduced drug efficacy. It is important to discuss your medication regimen and potential alternatives with your clinician or pharmacist.
This homozygous genotype is extremely rare in the general population.
Understanding the Variant and Gene
The CYP2D6 gene provides instructions for making an enzyme that belongs to the cytochrome P450 family, primarily located in the liver. This enzyme is responsible for the metabolism, or breakdown and activation, of approximately 20 to 25 percent of all clinically used medications, including antidepressants, antipsychotics, and certain pain relievers. The rs113926168 variant is a frameshift mutation, a type of genetic change that disrupts the normal reading frame of the gene's instructions. In this specific case, it leads to a non-functional enzyme product, meaning that individuals who carry this variant on both copies of their CYP2D6 gene, or in combination with other non-functional alleles, may have little to no CYP2D6 enzymatic activity. Because the gene is highly polymorphic, hundreds of different variants exist, but those that result in a null or non-functional enzyme are clinically significant because they can alter how a patient responds to standard drug doses.
Research and Pharmacogenomic Association
Research into CYP2D6 is central to the field of pharmacogenomics, which studies how genetic variation affects drug response. The association between rs113926168, known as the CYP2D6*6 allele, and altered drug metabolism is supported by established evidence in the clinical genetics community. Because the CYP2D6*6 allele is classified as a no-function allele, its presence is a key factor in predicting an individual’s metabolizer phenotype. Individuals classified as poor metabolizers due to their CYP2D6 genotype may experience significantly higher blood levels of drugs that require the enzyme for elimination, potentially increasing the risk of adverse side effects. Conversely, they may not receive the intended therapeutic benefit from prodrugs, which are medications that must be activated by the CYP2D6 enzyme to work. While the evidence linking specific CYP2D6 null alleles to metabolism is strong, clinical management must be personalized. Always discuss your pharmacogenomic test results and medication dosing with your healthcare provider or a clinical pharmacist before making any changes to your treatment plan.
What You Can Do With This Information
Genetic information regarding pharmacogenomics is a tool to help clinicians optimize therapy, but it is not a standalone diagnostic. If you have received results indicating you carry the rs113926168 variant, it is important to understand that this is only one piece of your overall metabolic profile. Because CYP2D6 is highly complex, your total enzyme activity depends on the combination of all variants present on both of your gene copies. You cannot use this information to self-diagnose or adjust your own medication dosages. Instead, use this data as a starting point for a conversation with your doctor or a pharmacist. They can interpret your results in the context of your current medications, health history, and other environmental factors that influence liver enzyme function. By sharing this information with your healthcare team, you ensure that your treatment plan is tailored to your specific genetic makeup, potentially reducing the risk of adverse reactions or therapeutic failure.
How common is this variant?
The rs113926168 variant is considered relatively rare in the general population, observed primarily in European populations with a minor allele frequency of approximately 0.01. It is rare or absent in many other global populations.
Frequently asked questions
Does having a poor metabolizer genotype mean a drug won't work for me?
Not necessarily. For some drugs, it means the medication is not activated efficiently, so it may not work as expected. For others, it means the drug stays in your system too long, which may increase the risk of side effects.
Should I stop taking my medication if I have this variant?
No. Never stop or change your medication dosage based on genetic information without consulting your doctor. Your clinician will weigh your genetic results alongside other factors like your health history and other medications you may be taking.
Is this test the same as a comprehensive pharmacogenomic panel?
rs113926168 is just one of many variants in the CYP2D6 gene. A comprehensive pharmacogenomic test typically looks at a much broader range of variants and copy number changes to provide a clearer picture of your overall enzyme function.
Can my metabolizer status change over time?
Your genetic genotype does not change. However, your phenotype, or how you actually metabolize drugs, can be influenced by other factors, such as drug-drug interactions where other medications inhibit the enzyme, or changes in liver health.
Sources & further reading
Educational information only, last refreshed 9/25/2026. 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 non-functional CYP2D6*41 splice defect associated with intermediate metabolizer phenotype affecting codeine, tamoxifen, and SSRI metabolism.