What Is Pharmacogenomics?

Pharmacogenomics (often abbreviated PGx) is the study of how an individual's genetic makeup affects their response to drugs. It combines pharmacology — the science of drugs — with genomics — the study of genes and their functions — to understand why the same medication can work well for one person but cause side effects or be ineffective for another.

Why Do People Respond Differently to the Same Drug?

When you take a medication, your body processes it through a series of biochemical steps: absorption, distribution, metabolism, and elimination. Many of these steps are carried out by enzymes — proteins encoded by your genes.

Variations in the genes that encode these enzymes can change how quickly or slowly you metabolize a drug. For example, some people carry genetic variants that make the enzyme CYP2D6 work much faster than normal (ultrarapid metabolizers), while others have variants that make it work slower or not at all (poor metabolizers).

These differences can have real clinical consequences. A poor metabolizer of CYP2D6 may experience toxic levels of codeine because they cannot convert it to morphine at the expected rate. An ultrarapid metabolizer of the same enzyme may convert codeine too quickly, potentially causing dangerous side effects.

Key Pharmacogenes

While hundreds of genes may influence drug response, a smaller set has strong enough clinical evidence to guide prescribing decisions. Some of the most well-studied pharmacogenes include:

• CYP2D6 — Metabolizes approximately 25% of all prescribed drugs, including many antidepressants, opioids, and antipsychotics.
• CYP2C19 — Affects the metabolism of clopidogrel (a blood thinner), certain antidepressants, and proton pump inhibitors.
• CYP2C9 — Influences warfarin metabolism and some anti-inflammatory drugs.
• DPYD — Determines how you process fluoropyrimidine chemotherapy drugs. Variants can cause severe toxicity.
• TPMT/NUDT15 — Affects thiopurine drug metabolism, used in autoimmune diseases and certain cancers.

How Is Pharmacogenomic Testing Done?

Clinical pharmacogenomic testing is performed in certified laboratories using blood or saliva samples. However, consumer DNA tests from services like 23andMe and AncestryDNA also capture many pharmacogenomically relevant genetic variants as part of their genotyping arrays. Learn more about the step-by-step testing process.

Services like DecodeMyBio can analyze the raw data from these consumer tests to extract pharmacogenomic information, mapping variants to established clinical guidelines from organizations like CPIC (Clinical Pharmacogenetics Implementation Consortium). Your consumer array also captures variants relevant to nutrient metabolism pathways — see our methylation testing guide for how genetic and biomarker data combine to assess metabolic health. If you already have raw data from a consumer test, see our guide to what to do with your 23andMe raw data. For a breakdown of how clinician-ordered panels like GeneSight compare to raw data analysis in terms of pricing and coverage, see the GeneSight cost, insurance & alternatives guide.

What Can Pharmacogenomics Tell You?

A pharmacogenomic report typically tells you your metabolizer phenotype for key drug-metabolizing enzymes: whether you are a normal, intermediate, poor, or ultrarapid metabolizer. This information can help your healthcare provider:

• Choose medications more likely to work for you
• Avoid drugs that may cause adverse reactions
• Adjust dosages based on your metabolic profile
• Understand why a past medication may not have worked

Limitations

Pharmacogenomics is one piece of the puzzle. Drug response is also influenced by age, weight, organ function, other medications, and environmental factors. Pharmacogenomic information should always be interpreted by a healthcare provider in the context of your complete medical history.

Consumer-grade analysis from raw DNA data also has inherent limitations compared to clinical-grade testing — see our Limitations page for details.

Get Your Pharmacogenomic Report

Ready to see how your genes may influence your medication response? Upload your DNA raw data from 23andMe, AncestryDNA, or other consumer tests to get your personalized Medication Safety Report. You can also read about how to interpret your report once you receive it.