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Pharmacogenomics

How your genes can change the way your body handles some medicines: genotype to metabolizer status, where the guidance comes from, and a result’s limits.

By the GeneMatrix editorial teamUpdated 5 min read

A man in his fifties, in glasses, reading a printed report at a kitchen table, an unlabeled pill organizer and a glass of water beside him.

In short

Some of your genes make the enzymes and transporters that handle certain medicines. Common variants in those genes can make you process a medicine more slowly or more quickly than usual. Published guidance, such as CPIC guidelines and FDA drug labels, tells prescribers when a result like that matters.

On this page
  1. What is pharmacogenomics?
  2. How does a gene change the way a medicine works?
  3. From your genotype to your metabolizer status
  4. How common are these variants?
  5. Where does the guidance come from?
  6. Examples where guidance exists
  7. What a PGx result can’t tell you
  8. How GenePGx works
  9. What to do next

What is pharmacogenomics?

Pharmacogenomics (often shortened to PGx) is the study of how the genes you inherited affect the way your body handles medicines. A pharmacogenomic test looks at a small, well-studied set of genes, not your whole genome.

Most of what a report covers falls into two groups of genes:

  • Processing genes. They make the enzymes that break a medicine down or switch it on, and the transporters that carry it into the liver. Variants here change how much of a medicine, or of its active form, is in your body.
  • Response genes. They affect how your body or your immune system reacts to a medicine. One immune-system gene, for example, is linked with a rare but serious reaction to one medicine.

Your genes don’t decide whether a medicine is right for you. They are one piece of information your prescriber can weigh.

How does a gene change the way a medicine works?

Take the cytochrome P450 enzymes, a family that includes CYP2D6 and CYP2C19. Many medicines rely on them to be broken down, and a few rely on them to be turned from an inactive form into the active one.[3][4]

If the versions of the gene you carry make a less active enzyme, a medicine can build up more than expected, or an inactive form may not be switched on as well. If they make a more active enzyme, the opposite can happen.

The same medicine can be processed more slowly, typically or more quickly, partly depending on the versions of these genes you carry.

From your genotype to your metabolizer status

A report doesn’t hand you raw DNA letters. A result is worked out in four steps:

  1. 1Your genotypeThe lab reads which versions of each gene you carry at the positions it tests. You have two copies of most genes, one from each parent.
  2. 2Star allelesKnown combinations of variants have standard names called star alleles, such as *1 or *2. Your pair of them is your diplotype.
  3. 3Activity scoreFor some genes, each star allele gets an activity value between 0 and 1, and the two values are added up into an activity score.[2]
  4. 4Metabolizer statusThe diplotype, or the score, is translated into a standard term for how active the enzyme is likely to be.[1]
The five metabolizer terms, as CPIC defines them for CYP2C19 (other enzymes use the same scale)
TermWhat it means
Poor metabolizerTwo copies that don’t work, so little or no enzyme activity.[3]
Intermediate metabolizerOne working copy and one that doesn’t work, so less activity than usual.[3]
Normal metabolizerTwo copies that work as usual.[3]
Rapid metabolizerOne usual copy and one that works more than usual.[3]
Ultrarapid metabolizerTwo copies that work more than usual.[3]

Genes linked with a specific reaction, such as HLA-B, are reported more simply: positive or negative for a particular variant.[1]

How common are these variants?

Very common. In a study of 487,409 people in the UK Biobank, researchers looked at 14 genes that have CPIC guidance and found that 99.5% of participants had a genotype that may mean an atypical response to at least one medicine.[10]

Where does the guidance come from?

A genetic result only matters for a medicine when good evidence links the two. Two public sources set that evidence out:

  • CPIC guidelines. The Clinical Pharmacogenetics Implementation Consortium, set up in 2009, publishes freely available, evidence-based, peer-reviewed guidelines on how a genetic result can be used for specific medicines.[8]
  • FDA drug labels. The FDA keeps a public table of medicines whose labeling includes pharmacogenomic information, such as differences in how much of a medicine reaches the body, or the risk of a side effect.[9]

Examples where guidance exists

CPIC rates each of these gene and medicine pairs level A.[7] The table says only that guidance exists and what the gene does. It isn’t advice about any medicine.

Four gene and medicine pairs with CPIC guidance
GeneMedicineWhat the gene does here
CYP2C19clopidogrelHelps turn the medicine into its active form.[3]
CYP2D6codeineHelps process the medicine in the body.[4]
SLCO1B1simvastatinMakes a transporter that carries the medicine into the liver.[5]
HLA-BabacavirAn immune-system gene. One variant, HLA-B*57:01, is linked with a higher risk of a hypersensitivity reaction.[6]

Pharmacogenomic results describe how your body is likely to process certain medicines. They do not tell you whether a medicine will work for you, and they are not dosing instructions. Never start, stop or change a medication because of a genetic result. Bring it to the prescriber who manages your medicines.

What a PGx result can’t tell you

  • Not every medicine has guidance. It exists for a limited set of gene and medicine pairs. For many medicines there is none yet.
  • Genes are one factor among many. Other medicines you take, your age, and how your liver and kidneys are working can all change how you respond.
  • Genotyping can miss rare variants. A genotyping test looks for a set of known variants chosen in advance.[11] People of non-European ancestry carry more variants that may affect these genes, and current definitions miss many of them.[10]
  • Some genes are harder to read. CYP2D6 can have extra or missing copies. When a test can’t tell how many copies there are, the result may assume the usual two.[2]
  • A result can’t say a medicine will help you. It describes how you are likely to process a medicine, not whether it will work for you.

How GenePGx works

  1. Collect at home. You give a saliva sample with the kit and send it back.
  2. Genotyped in the lab. Checks selected known variants in 15 genes, plus CYP2D6 copy number, by genotyping. It tests genes named in CPIC prescribing guidelines for 56 medicines (checked September 29, 2026).
  3. One report, four views. Everyday medicines, pain medicines, mental-health medicines, and a supplement view.
  4. Read it with your prescriber. The report is written to be read with the clinician who manages your medicines.

The supplement section is never billed to insurance.

What to do next

Curious whether a medicine has published guidance? Try the Medication Check, or read how pharmacogenomics works at GeneMatrix.

Sources

  1. [1]Standardizing terms for clinical pharmacogenetic test results: consensus terms from the Clinical Pharmacogenetics Implementation Consortium (CPIC). Genetics in Medicine, 2017. Accessed .
  2. [2]Standardizing CYP2D6 genotype to phenotype translation: consensus recommendations from CPIC and DPWG. Clinical and Translational Science, 2020. Accessed .
  3. [3]CPIC guideline for CYP2C19 genotype and clopidogrel therapy: 2022 update. Clinical Pharmacology & Therapeutics, 2022. Accessed .
  4. [4]CPIC guideline for CYP2D6, OPRM1, and COMT genotypes and select opioid therapy. Clinical Pharmacology & Therapeutics, 2021. Accessed .
  5. [5]CPIC guideline for SLCO1B1, ABCG2, and CYP2C9 genotypes and statin-associated musculoskeletal symptoms. Clinical Pharmacology & Therapeutics, 2022. Accessed .
  6. [6]CPIC guidelines for HLA-B genotype and abacavir dosing. Clinical Pharmacology & Therapeutics, 2012. Accessed .
  7. [7]Genes and drugs: CPIC levels for each gene and drug pair. Clinical Pharmacogenetics Implementation Consortium (CPIC). Accessed .
  8. [8]The Clinical Pharmacogenetics Implementation Consortium: 10 years later. Clinical Pharmacology & Therapeutics, 2020. Accessed .
  9. [9]Table of Pharmacogenomic Biomarkers in Drug Labeling. U.S. Food and Drug Administration. Accessed .
  10. [10]Pharmacogenetics at scale: an analysis of the UK Biobank. Clinical Pharmacology & Therapeutics, 2021. Accessed .
  11. [11]Recommendations for clinical CYP2D6 genotyping allele selection: a joint consensus recommendation (AMP, CAP, DPWG, ESPT). The Journal of Molecular Diagnostics, 2021. Accessed .

How we write and source these pieces: our editorial policy.

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PGxPharmacogenomic results describe how your body is likely to process certain medicines. They do not tell you whether a medicine will work for you, and they are not dosing instructions. Never start, stop or change a medication because of a genetic result. Bring it to the prescriber who manages your medicines.

NoteThe supplement section is never billed to insurance.

LabOur genetic tests are laboratory-developed tests performed in our own CLIA-certified laboratory. New York is the exception: orders shipped there are completed through a physician order or a reference laboratory permitted in New York. Our genetic tests have not been cleared or approved by the FDA. Results describe inherited traits and risks and are meant to inform decisions you make with your clinician. They are not a diagnosis.