Understand results guide

Pharmacogenomics

Pharmacogenomics (PGx)^** is about how a patient's genetics may affect the way they process specific medications. This guide covers reports related to enzyme metabolizer status, transporter function, and medication response, and what each means for prescribing.

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Orienting to the report

Each Pharmacogenetic report names the gene, your patient's metabolizer or transporter status for it, and the medications that status affects. Reports focus on high-evidence gene-drug relationships with actionable clinical guidance. For certain medications, a Medication Insight is also provided that predicts the genetic impact on effectiveness or side effect risk.

Ask your patient to print the clinician summary from their account. It lists every gene tested, their result, and the potentially impacted medications in a single table.

The GLP-1 Medication Response report works differently. It is an interactive tool, based on 23andMe research, that estimates how a patient may respond to a GLP-1 medication.

Key framing for clinical use: PGx results are one piece of a patient's drug response picture. Age, weight, organ function, and drug interactions all shape how a medication performs, and should be weighed together when prescribing.

**Pharmacogenetic report** · Metabolizer status for one gene and the medications it affects

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Result outcomes

Metabolizer

Applies to enzyme-encoding genes such as CYP2C19 and DPYD, describing how quickly a patient processes a drug.

What this means

Little to no functional enzyme activity. For active drugs, the drug clears slowly, potentially reaching toxic levels at standard doses. For prodrugs, the drug may not be converted to its active form and will likely lack efficacy.

Clinical considerations

Refer to the report for confirmatory testing requirements. Most CYP2C19 results do not require confirmatory testing
Review any genotype-based prescribing guidance for the specific gene-drug pair from the FDA or from guidelines including CPIC. ClinPGx consolidates these sources in one place
ClinPGx ↗

What this means

Reduced but not absent enzyme activity. Drugs clear somewhat more slowly (or prodrugs activate less efficiently) than in a normal metabolizer. Clinical significance varies substantially by gene-drug pair.

Clinical considerations

Refer to the report for confirmatory testing requirements. Most CYP2C19 results do not require confirmatory testing
Review any genotype-based prescribing guidance for the specific gene-drug pair from the FDA or from guidelines including CPIC. ClinPGx consolidates these sources in one place
ClinPGx ↗

What this means

Enzyme activity is within the expected range; standard dosing recommendations apply. This is the most common result.

Clinical considerations

Not all variants are covered by this test; more comprehensive pharmacogenomic testing may be appropriate in some cases, particularly for DPYD before fluoropyrimidine chemotherapy
Normal metabolizer status does not rule out adverse drug reactions from other causes (drug interactions, organ dysfunction, non-genetic factors)

What this means

Above-normal enzyme activity, faster than typical but not at the extreme end of the spectrum. Occurs when one allele is normal-function and the other is increased-function. Active drugs clear more quickly than average, which can reduce how much reaches its target at standard doses.

Clinical considerations

Refer to the report for confirmatory testing requirements. Most CYP2C19 results do not require confirmatory testing
Review any genotype-based prescribing guidance for the specific gene-drug pair from the FDA or from guidelines including CPIC. ClinPGx consolidates these sources in one place
ClinPGx ↗

What this means

Markedly higher-than-normal enzyme activity. For active drugs, standard doses may be subtherapeutic.

Clinical considerations

Refer to the report for confirmatory testing requirements. Most CYP2C19 results do not require confirmatory testing
Review any genotype-based prescribing guidance for the specific gene-drug pair from the FDA or from guidelines including CPIC. ClinPGx consolidates these sources in one place
ClinPGx ↗

Transport

Applies to transporter genes such as SLCO1B1. Rather than enzyme activity, these results describe how efficiently a drug is moved in or out of specific tissues and cells. When transport is disrupted, a drug may abnormally accumulate either in the plasma or inside specific organs, increasing the risk of toxicity or treatment failure.

What this means

Transporter activity is within the expected range; standard dosing recommendations apply. This is the most common result.

Clinical considerations

Not all variants are covered by this test; more comprehensive pharmacogenomic testing may be appropriate
Normal transporter function does not rule out adverse drug reactions from other causes (drug interactions, organ dysfunction, non-genetic factors)

What this means

The transporter moves drugs less efficiently. This can lead to abnormal drug levels in the body, such as a drug accumulating in the bloodstream because it cannot be transported into its target cells, or failing to reach the target tissue at all.

Clinical considerations

Refer to the report for confirmatory testing requirements. Most SLCO1B1 results do not require confirmatory testing
Review any genotype-based prescribing guidance for the specific gene-drug pair from the FDA or from guidelines including CPIC. ClinPGx consolidates these sources in one place
ClinPGx ↗

What this means

Severely impaired transporter activity. This can lead to abnormal drug levels in the body, such as a drug accumulating in the bloodstream because it cannot be transported into its target cells, or failing to reach the target tissue at all.

Clinical considerations

Refer to the report for confirmatory testing requirements. Most SLCO1B1 results do not require confirmatory testing
Review any genotype-based prescribing guidance for the specific gene-drug pair from the FDA or from guidelines including CPIC. ClinPGx consolidates these sources in one place
ClinPGx ↗

Medication response

What this means

The GLP-1 Medication Response is an interactive tool that combines genetics with demographics and medical history to estimate both weight loss and nausea likelihood for semaglutide and tirzepatide based on data from 23andMe research participants. The tool was built based on findings from a 2026 Nature publication.

Clinical considerations

Most useful as a shared decision-making tool, particularly when a patient is weighing whether to initiate a GLP-1 medications, or when they've had a suboptimal response to one
A lower predicted weight loss or increased risk for nausea does not mean the medication should be avoided
The tool is based on emerging science and should not be used on its own to make medical decisions.

Pharmacogenetics

CYP2C19 Drug Metabolism3 variants
Medication insight: Citalopram (Celexa®)
Medication insight: Clopidogrel (Plavix®)
DPYD Drug Metabolism2 variants
SLCO1B1 Drug Transport1 variant
Medication insight: Simvastatin (Flolipid®, Zocor®)

Medication response

GLP-1 Medication Response2 variants

Other pharmacogenomic-related reports

Genotyping

G6PD DeficiencyG6PD · 2 variants
Hereditary ThrombophiliaF2/F5 · 2 variants

Sequencing

G6PD DeficiencyG6PD
Hereditary ThrombophiliaF2/F5
Malignant HyperthermiaCACNA1S/RYR1

Medication spotlights

Deep dives on gene-drug relationships with high clinical relevance and strong guideline support.

Clinical resources

Sample reports, clinical downloads, educational videos, and external references all collected in one place.

Go to Resources →

Questions about a specific result? Contact our clinical team at medical@23andme.com

Frequently asked questions

Pharmacogenomics (PGx) is the study of how genetic variants influence the way a person processes and responds to medications. The terms "pharmacogenetics" and "pharmacogenomics" are often used interchangeably; pharmacogenetics more often refers to single-gene variant testing, while pharmacogenomics is used in the broader context of whole-genome approaches or genetics-guided drug development.

Most pharmacogenetic variants are inherited differences that can affect how the body processes a medication or how the body responds to it. Researchers have identified variants across dozens of genes that may affect hundreds of medications.

23andMe's Pharmacogenetic reports cover three genes: CYP2C19 (drug metabolism), DPYD (drug metabolism), and SLCO1B1 (drug transport). These reports identify variants that may affect how efficiently certain medications are processed, which can influence both efficacy and the risk of side effects.

The FDA requires confirmatory testing for some pharmacogenetic results before taking medical action, while others do not carry this requirement. The distinction reflects the level of analytical evidence supporting each report. For reports where confirmatory testing is not required, 23andMe has completed additional analytical validation studies using blinded samples, demonstrating accuracy that satisfies FDA requirements for direct clinical use without a separate confirmation step.

These results should always be interpreted in the context of the full clinical picture, and treatment decisions should involve the patient's care team. For more details on the analytical studies performed for these reports, see our package insert.

Package insert ↗

Not necessarily. A pharmacogenetic finding that suggests caution does not automatically mean a patient's current regimen needs to change, especially if they are tolerating it well without adverse effects.

For example, a patient with an SLCO1B1 reduced-function variant who is tolerating low-dose simvastatin without musculoskeletal symptoms may not need an immediate switch. However, the finding should be documented in their medication record and considered if the dose increases or symptoms develop.

No. A normal result for a specific gene only means the genetic contribution from that gene is likely within the expected range, although other variants not tested may be present. It does not address other pharmacogenetic genes, non-genetic factors such as organ function, age, or co-medications, or drug interactions that can functionally alter drug processing regardless of genotype. Pharmacogenetic results are one input into prescribing decisions, not a comprehensive drug compatibility screen.

Yes. The FDA has issued a boxed warning for fluoropyrimidine medications (5-FU and capecitabine) noting the risk of severe and potentially fatal adverse reactions in patients with DPYD deficiency, and recommends testing for DPYD deficiency prior to initiating therapy with these agents.

Of note, the 23andMe DPYD Drug Metabolism report only tests for select variants. More comprehensive DPYD genotyping through a clinical laboratory should be considered for these patients.

Important test information

** Pharmacogenetic reports: 23andMe PGS Pharmacogenetics reports: The 23andMe test uses qualitative genotyping to detect 3 variants in the CYP2C19 gene, 2 variants in the DPYD gene and 1 variant in the SLCO1B1 gene in the genomic DNA of adults from saliva for the purpose of reporting and interpreting information about the processing of certain therapeutics to inform discussions with a healthcare professional. It does not describe if a person will or will not respond to a particular therapeutic. Our CYP2C19 Pharmacogenetics report provides certain information about variants associated with metabolism of some therapeutics and provides interpretive drug information regarding the potential effect of citalopram and clopidogrel therapy. Our SLCO1B1 Pharmacogenetics report provides certain information about variants associated with the processing of some therapeutics and provides interpretive drug information regarding the potential effect of simvastatin therapy. Our DPYD Pharmacogenetics report does not describe the association between detected variants and any specific therapeutic. Results for DPYD and certain CYP2C19 results should be confirmed by an independent genetic test prescribed by your own healthcare provider before taking any medical action. Warning: Test information should not be used to start, stop, or change any course of treatment and does not test for all possible variants that may affect metabolism or protein function. The PGS test is not a substitute for visits to a healthcare professional. Making changes to your current regimen can lead to harmful side effects or reduced intended benefits of your medication, therefore consult with your healthcare professional before taking any medical action. For important information and limitations regarding Pharmacogenetic reports, visit 23andme.org/en-ca/shop/test-info/pharmacogenetics/

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Statin-Associated Musculoskeletal Symptoms

Antidepressant Metabolism: SSRIs & TCAs

Fluoropyrimidine Chemotherapy Toxicity

Clopidogrel and Antiplatelet Therapy

Clinical resources