Thiopurine S-methyltransferase
TPMT helps inactivate thiopurines, including azathioprine, mercaptopurine, and thioguanine. Reduced function can increase susceptibility to severe bone-marrow toxicity. The CPIC 2025 update interprets TPMT and NUDT15 together.[1]
Gene2Rx uses definitions covering 49 named TPMT star alleles, built from 45 variants in Gene2Rx definitions. Results depend on the variants available in your upload.
Star alleles (like *1, *2, *4) are standardized names for distinct versions of a pharmacogene. *1 is the reference; other numbers identify distinct allele definitions. A higher number does not mean lower function.
You inherit one allele from each parent, so your genotype is a pair (e.g. *1/*4). The pair determines your predicted phenotype — for example, whether you metabolize a drug at a normal, decreased, or no-function rate.
PharmVar is the international registry that defines and curates these allele names. Gene2Rx uses the supported definitions summarized here. Coverage depends on the variants present in your input; this is not a guarantee that every cataloged allele can be identified.
This list contains 3 medications with TPMT information from the sources shown below. Evidence and report eligibility differ by drug; each page explains its scope and limitations.
These branded medications include at least one active ingredient whose metabolism or action involves TPMT. Each links to its full pharmacogenetic breakdown.
A Gene2Rx report interprets supported variants in the context of your data and purchased report. Missing or uncertain calls may prevent an assessment.
Get your report Look up a medicationInformational only, not medical advice. The presence of a TPMT pharmacogenetic guideline does not mean every patient needs to change their dose. Never start, stop, or change a medication without talking to your prescribing clinician.