Your biology
Peptides and your genome. Mostly hype, with a few real exceptions.
The urge to "check your genes before starting a peptide" is borrowed from small-molecule pharmacology. And it mostly doesn't transfer. For the experimental peptides, there are essentially zero human pharmacogenomic studies. We went looking. But a handful of markers turned out to be genuinely real, and they're worth knowing before you start. Here's what we found.
Two things we had wrong at first
CYP gene panels don't apply to peptides
Peptides are broken down by proteases and cleared by the kidneys, not by the liver's CYP450 enzymes that classical drug-gene tests are built around. So a consumer CYP2D6/2C19 'pharmacogenomic' panel has essentially no substrate to act on in a peptide. It tells you almost nothing about how you'll handle one.
MTHFR is not a drug-metabolizing gene
The single most-hyped 'you must test this' gene isn't a drug-gene at all, it's a folate-cycle enzyme. Roughly half the population carries a variant, and the American College of Medical Genetics explicitly recommends against testing it routinely. If homocysteine matters to you, measure homocysteine, don't genotype.
The one lab that actually gates things
The lab that actually matters before nearly any peptide isn't a gene panel, it's kidney and liver function (eGFR, creatinine, and LFTs), because that's what governs how fast you clear it.
Where genetics is actually real
Five markers we think are worth your attention. Graded by how solid the link actually is, from established human pharmacology down to mechanistic reasoning.
RET / MEN2
GLP-1s (semaglutide, tirzepatide)
The firmest genetic statement in the entire field: a germline RET mutation, MEN2, or a personal/family history of medullary thyroid carcinoma.
A boxed-warning contraindication, do not use. (Routine calcitonin/ultrasound screening is NOT recommended without those risk factors.)
ATP7B (Wilson's disease)
GHK-Cu
GHK-Cu delivers copper; ATP7B is the body's copper-handling gene. In Wilson's disease or copper-overload conditions, a copper-delivering peptide runs against the entire treatment.
A relative contraindication for injected GHK-Cu in copper-overload conditions. Topical exposure is far lower. The strongest real genetic caution here, though never GHK-Cu-tested.
m.1382A>C (K14Q)
MOTS-c
MOTS-c is encoded inside mitochondrial DNA, so this variant literally changes the peptide's own sequence, producing a weaker, near-inactive version. East-Asian-specific; tracks with higher type-2-diabetes risk in men.
The unusually real case, but it's the genetics of your own peptide, not proof of how you'd respond to an injection (no completed human MOTS-c trial exists).
GHR exon-3 deletion (d3-GHR)
GH-axis (tesamorelin, ipamorelin, CJC-1295, sermorelin)
The d3 growth-hormone-receptor variant produces a 1.7–2× stronger GH response; carriers needed roughly 25% less growth hormone in dosing studies.
A genuine pharmacogenomic marker, but earned on recombinant growth hormone, not the secretagogues, so applying it to these peptides is reasoned extrapolation.
VEGF / angiogenesis pathway
BPC-157 & TB-500
Both push VEGF and angiogenesis, new blood-vessel growth, the same pathway tumors exploit to feed themselves.
Not a gene test you'd run, but the reason cancer screening is advised before use, especially with a personal or family cancer history.
Look yourself up
If you have a 23andMe file or a raw-genome export, you can look some of these up by rsID. MOTS-c's K14Q is rs111033358; the BPC-157 / TB-500 angiogenesis story runs through VEGF variants like rs699947 and rs3025039. Others. RET/MEN2, ATP7B (Wilson's), the d3-GHR deletion, aren't reliably on a consumer chip and need clinical sequencing. Treat whatever you find as a flag worth investigating, not a verdict. The science here is genuinely thin.
Blood markers that actually matter
Honestly, these are more useful than a gene panel for almost everyone. Because these are numbers you can actually move and track over time.
The real titration and safety biomarker for the GH peptides. The tesamorelin label says to monitor it and consider stopping if it runs persistently high. An already-high baseline means no headroom.
For GLP-1s and the GH peptides (which are diabetogenic). C-peptide also gauges the β-cell reserve that incretins need in order to work.
Before systemic GHK-Cu, to rule out a copper-handling problem. Topical use doesn't need it.
The universal gate. Peptides clear renally and hepatically, so this matters across the board, far more than any gene panel.
Our honest bottom line
Peptide pharmacogenomics is, with a few exceptions, a nascent and largely theoretical field. The instinct to 'check your genes before starting a peptide' is borrowed from small-molecule pharmacology, and it mostly doesn't transfer. So: skip the gene-panel hype. Watch the markers that are actually real. IGF-1 for the GH peptides, HbA1c and C-peptide for GLP-1s, a copper panel before systemic GHK-Cu, and, above all, your kidney and liver function. Treat any peptide-pharmacogenomic claim as provisional until the literature catches up.
Our sources
Cross-reference any of this against a specific compound on the graded index. Nothing here is medical advice. This is education only -- talk to a licensed clinician before acting on any of it.