There is no universal checklist, but medicine already keeps one for approved peptide drugs: contraindications on the label. For semaglutide that means certain thyroid cancer histories and prior severe reactions, with added caution in pregnancy, pancreatitis history, and kidney or eye disease. For unregulated research peptides, the exclusion logic inverts — with no safety data, there is no group in whom the risk is characterized.
How labels define who is excluded
Every approved drug ships with a contraindications section — the list of people in whom regulators concluded the risk outweighs any benefit. The Ozempic (semaglutide) label is a concrete example of how specific this gets:
- Personal or family history of medullary thyroid carcinoma (MTC), or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) — an absolute contraindication tied to the boxed warning about thyroid C-cell tumors seen in rodent studies.
- Prior serious hypersensitivity reaction to the drug or its components, because anaphylaxis and angioedema have been reported.
Beyond hard contraindications, the label's warnings identify groups where clinicians weigh the drug more carefully: people with a history of pancreatitis (acute pancreatitis, including fatal cases, has occurred with GLP-1 drugs), gallbladder disease, diabetic retinopathy (complication rates were higher on treatment), and anyone prone to volume depletion, since dehydration from GI side effects has caused acute kidney injury — covered in depth on the kidney risk page.
Pregnancy, breastfeeding, and children
Pregnancy is where trial evidence is thinnest by design: pregnant women are excluded from drug trials, so human safety data come only from animal studies and registries. For semaglutide, animal data showed fetal harm, and the label directs that the drug be discontinued at least two months before a planned pregnancy because of its long washout period.
That is the state of knowledge for the best-studied peptide drug. For research peptides there are no reproductive toxicity packages, no pregnancy registries, and no pediatric data of any kind — which is why clinicians treat pregnancy, breastfeeding, and childhood as categorical exclusions for experimental compounds rather than judgment calls.
People with organ disease or complex medication lists
Trial populations are screened; real-world users are not. Several groups consistently sit outside the evidence base that peptide data rest on:
- Significant kidney or liver disease — trials stratify or exclude by baseline eGFR and liver status, so people with advanced organ disease are using the drug beyond the studied population (see liver and kidney pages).
- Active endocrine cancers or strong family cancer histories, per the MTC/MEN 2 pattern above.
- People on interacting therapies — for example, GLP-1 drugs slow gastric emptying and can amplify hypoglycemia risk when combined with insulin or sulfonylureas, a labeled interaction managed by dose adjustment in clinical care and unmanaged outside it.
Athletes subject to anti-doping rules
Competitive athletes face a separate, non-medical reason for avoidance: most peptides discussed online are banned in sport. The WADA Prohibited List prohibits peptide hormones, growth factors, and their mimetics (class S2) at all times, and its S0 class bans any substance lacking regulatory approval for human therapeutic use — explicitly naming BPC-157 as an example. Under the World Anti-Doping Code's strict-liability principle, an athlete is responsible for what is in a vial even when the label was wrong — a hard problem when unregulated products carry no verified statement of contents.
Anyone relying on unverified sources
Finally, the risk calculus changes for anyone whose only access is gray-market product. The FDA's communication on unapproved GLP-1 drugs records hospitalizations from dosing errors with compounded semaglutide and products built on unevaluated salt forms — failures of the supply chain, not the molecule. Groups with the least margin for such errors (older adults, people with organ disease, people on many medications) are the same groups labels already flag, which is why the two lists overlap so heavily.