SAFETY, SIDE EFFECTS & WHO SHOULD NOT USE PEPTIDES

Who Should Not Use Peptides — Contraindications and Screening

By G1 Peptides · Medically reviewed by the G1 Peptides clinical team · Updated September 24, 2026 · 2 min read

THE SHORT ANSWER

Peptides are not for everyone. Pregnancy and breastfeeding rule out essentially all of them; active cancer rules out growth-hormone and tissue-repair peptides; a personal or family history of medullary thyroid cancer rules out GLP-1 medications; uncontrolled cardiovascular disease rules out PT-141. A provider's screening exists to catch these before a prescription is written.

Absolute stops (for essentially every peptide)

Pregnancy, trying to conceive, or breastfeeding. None of the peptides discussed here have safety data in pregnancy, and several act on hormonal or growth signalling. Providers will not prescribe, and anyone who becomes pregnant on a protocol should stop and call.
Known allergy to the peptide or to benzyl alcohol (the preservative in bacteriostatic water — sterile water is a workaround for the latter).
Under 18.

By peptide family

GLP-1 and incretin peptides

Personal or family history of medullary thyroid carcinoma or MEN2 — boxed-warning contraindication on the approved products, applied to compounded versions too.
History of pancreatitis — relative contraindication; discussed case by case.
Gastroparesis or severe gastrointestinal disease — these drugs slow the gut further.
Type 1 diabetes or insulin/sulfonylurea use without coordination — hypoglycemia risk.
Planned surgery under anesthesia — the slowed stomach emptying is an aspiration risk; most anesthesiologists ask for a hold of a week or more before elective procedures.
History of eating disorders — discussed carefully.

Growth-hormone secretagogues

Active cancer or a recent cancer history — these raise IGF-1, a growth signal. Providers generally want several years clear and oncology input.
Uncontrolled diabetes — GH raises glucose; tesamorelin's trials showed modest glucose increases (Falutz 2007).
Open growth plates (adolescents) and active proliferative diabetic retinopathy.
Acromegaly or a pituitary tumour.

Tissue-repair peptides (BPC-157, TB-500)

Active cancer — both are studied for promoting blood-vessel growth, which is desirable in a healing tendon and undesirable in a tumour. This is precautionary; no human data shows harm, but no provider takes the chance.

GHK-Cu

Wilson's disease or other copper-handling disorders.

PT-141

Uncontrolled hypertension or significant cardiovascular disease — it causes transient blood-pressure increases.
Concurrent use of drugs that lower blood pressure needs review.

Semax and selank

Few hard contraindications; semax is used cautiously with seizure disorders and bipolar disorder because of its activating effect.

Kisspeptin, oxytocin

Hormone-sensitive conditions and reproductive plans need specific discussion — kisspeptin drives the reproductive axis directly.

What screening looks like

A good consultation asks about all of the above directly — cancer history in you and your family, thyroid disease, pancreatitis, heart disease, blood pressure, diabetes, psychiatric history, pregnancy plans, and a complete medication and supplement list. Labs are ordered when they change the decision: IGF-1 and glucose for GH peptides, thyroid and a metabolic panel for GLP-1s.

If something on this page applies to you, it does not necessarily mean no peptide therapy at all — it usually means a different compound or extra monitoring. That is a conversation for a free consultation.

FREQUENTLY ASKED

Can I take peptides with my other medications?

Usually, but it depends on the peptide and the medication. GLP-1s slow gastric emptying, which changes how oral drugs absorb and matters especially for insulin and sulfonylureas. Growth-hormone peptides affect glucose. Bring a complete medication list to your consultation.

Is there an age limit?

Peptides are prescribed to adults. Growth-hormone secretagogues are not prescribed to people whose growth plates are still open, and providers are conservative with anyone under 25. There is no upper age limit, but screening becomes more thorough.

What if I develop a condition after starting?

Tell your provider. A new cancer diagnosis, pregnancy, a cardiac event, or a new medication can change what is appropriate, and stopping most peptides is straightforward.

SOURCES

This article is educational and is not medical advice. Peptides are prescription medications; whether any of them is appropriate for you is a decision for a licensed provider who knows your history.