How Genetics Affect Your Medications
You've probably noticed that the same medication can work perfectly for one person and cause side effects — or do nothing — for someone else. That isn't random. A major reason is genetics: inherited variants in the genes that encode drug- metabolizing enzymes change how quickly your body activates, processes, or clears a medication.
Most drug metabolism runs through a family of liver enzymes called cytochrome P450 (CYP450). Genes like CYP2D6, CYP2C19, and CYP2C9 each have common variants that can make you a poor, intermediate, normal, rapid, or ultrarapid metabolizer. A poor metabolizer clears a drug slowly, increasing the risk of side effects at a standard dose. An ultrarapid metabolizer may clear it so fast that the drug never reaches a therapeutic level — or, for prodrugs like codeine, converts too much too quickly, creating a safety risk.
The Clinical Pharmacogenetics Implementation Consortium (CPIC) reviews this evidence and publishes peer-reviewed guidelines for specific drug-gene pairs. CPIC Level A means the evidence is strong enough that genetic results should change prescribing decisions. The medications listed below all have CPIC-level guidance, and each page explains the relevant gene, how metabolizer status shifts efficacy or safety, and what the guidelines recommend. To understand the broader science, read What Is Pharmacogenomics?
If you have raw DNA data from 23andMe or AncestryDNA, you can upload it to DecodeMyBio and get a personalized report covering all the medications below — plus dozens more. See a sample Medication Safety Report to understand the format before you upload.
Medication Pages
Clopidogrel (Plavix)
CPIC Level AAntiplatelet therapy — CYP2C19 metabolizer status affects activation of this prodrug
Primary gene: CYP2C19
Codeine
CPIC Level AOpioid prodrug — CYP2D6 metabolizer status determines morphine conversion and safety
Primary gene: CYP2D6
Fluoxetine (Prozac)
CPIC Level ASSRI antidepressant — CYP2D6 metabolizer status affects drug exposure and clinical response
Primary gene: CYP2D6
Escitalopram (Lexapro)
CPIC Level ASSRI antidepressant — CYP2C19 metabolizer status affects drug exposure and side-effect risk
Primary gene: CYP2C19
Sertraline (Zoloft)
CPIC Level ASSRI antidepressant — CYP2C19 contributes to metabolism; dosing guidance available
Primary gene: CYP2C19
Paroxetine (Paxil)
CPIC Level ASSRI antidepressant — CYP2D6 metabolizer status affects drug exposure; paroxetine also inhibits CYP2D6
Primary gene: CYP2D6
Atomoxetine (Strattera)
CPIC Level ANon-stimulant ADHD medication — CYP2D6 poor metabolizers can have up to 10-fold higher drug exposure
Primary gene: CYP2D6
Aripiprazole (Abilify)
CPIC Level AAtypical antipsychotic — CYP2D6 poor metabolizers have ~80% higher exposure; FDA labeling recommends dose reduction
Primary gene: CYP2D6
Venlafaxine (Effexor)
CPIC Level ASNRI antidepressant — CYP2D6 affects parent-to-metabolite ratio; both parent drug and metabolite are active
Primary gene: CYP2D6
Amitriptyline (Elavil)
CPIC Level ATricyclic antidepressant — CYP2C19 and CYP2D6 together determine metabolism; CPIC recommends dose adjustments for both genes
Primary gene: CYP2C19 + CYP2D6
Simvastatin (Zocor)
CPIC Level AStatin therapy — SLCO1B1 genotype affects myopathy risk and recommended dose limits
Primary gene: SLCO1B1
Rosuvastatin (Crestor)
CPIC Level AStatin therapy — two genes (SLCO1B1 + ABCG2) affect drug exposure and safety
Primary gene: SLCO1B1 + ABCG2
Warfarin (Coumadin)
CPIC Level AAnticoagulant therapy — CYP2C9 and VKORC1 genotypes together guide dosing
Primary gene: CYP2C9 + VKORC1
Celecoxib (Celebrex)
CPIC Level ANSAID pain relief — CYP2C9 poor metabolizers have significantly higher drug exposure and risk
Primary gene: CYP2C9
Metoprolol (Lopressor, Toprol-XL)
CPIC DPWGBeta-blocker — CYP2D6 metabolizer status affects drug exposure, heart rate, and blood pressure response
Primary gene: CYP2D6
Omeprazole (Prilosec)
CPIC Level AProton pump inhibitor — CYP2C19 metabolizer status affects acid suppression and H. pylori eradication rates
Primary gene: CYP2C19
Ondansetron (Zofran)
CPIC Level AAnti-nausea medication — CYP2D6 ultrarapid metabolizers may have reduced efficacy due to faster clearance
Primary gene: CYP2D6
Pantoprazole (Protonix)
CPIC Level AProton pump inhibitor — CYP2C19 genotype affects acid suppression efficacy and long-term exposure
Primary gene: CYP2C19
Tamoxifen (Nolvadex)
CPIC Level ABreast cancer therapy — CYP2D6 metabolizer status affects conversion to active metabolite endoxifen
Primary gene: CYP2D6
Tramadol (Ultram)
CPIC Level AOpioid analgesic prodrug — CYP2D6 metabolizer status determines conversion to active O-desmethyltramadol
Primary gene: CYP2D6
Check Your Medication Interactions
If you have raw DNA data from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA, you can upload it to DecodeMyBio. Your Medication Safety Report checks over 100 drug-gene interactions across 13 pharmacogenes, identifying any medications where your genetics may warrant a conversation with your prescriber. You can preview a sample report to see the format.
Pharmacogenomic information is one factor among many in medication decisions. Drug response also depends on age, weight, organ function, other medications, and environmental factors. See our Limitations page for a complete discussion. Always consult your healthcare provider before making medication changes.