Safety
Side effects reported in peptide clinical research
The side effects of peptides follow their receptors. GLP-1 drugs mainly cause gastrointestinal symptoms; growth hormone secretagogues cause fluid retention and raise blood sugar; melanocortin agonists cause nausea, flushing and skin darkening. For compounds without human trials, the side effects are simply unknown.
Incretin and glucagon agonists
Semaglutide, tirzepatide, retatrutide and related drugs most often cause nausea, diarrhoea, vomiting and constipation, especially during dose escalation. Less common but serious risks on approved labels include pancreatitis, gallbladder disease, kidney injury from dehydration and, with insulin or sulfonylureas, low blood sugar. Approved long-acting GLP-1 agonists carry a boxed warning about thyroid C-cell tumours seen in rodents. Glucagon-containing agonists also raise resting heart rate.
Growth hormone axis
Compounds that raise GH and IGF-1 (sermorelin, tesamorelin, CJC-1295, ipamorelin, GHRP-2, GHRP-6, hexarelin, MK-677) can cause fluid retention, joint pain, tingling or carpal tunnel symptoms, and higher fasting glucose with reduced insulin sensitivity. Ghrelin-receptor agonists increase appetite, and some raise cortisol and prolactin. A phase 2b trial of MK-677 in older adults recovering from hip fracture was stopped early because of a heart failure signal.
Melanocortin agonists
Bremelanotide caused nausea in about 40% of trial participants, along with flushing, headache and transient blood pressure increases. Repeated use of melanocortin agonists darkens skin and moles. Unregulated melanotan II use has been associated with case reports of melanoma, priapism and kidney injury.
Compounds without human trials
For BPC-157, TB-500 fragments, MOTS-c, KPV, dihexa, the bioregulators and many others, there are no controlled human safety data. Absence of reported side effects in that situation means nobody has looked systematically, not that the compound is safe.
Risks that come from the product, not the peptide
- Wrong identity or amount. Independent tests of grey-market peptides have found products with the wrong peptide, much less or much more than labelled, or none at all.
- Contamination. Endotoxin, bacteria and residual solvents are not controlled in research-grade products.
- Injection risks. Non-sterile technique can cause abscesses and infections.
- Counterfeits. Regulators have reported counterfeit versions of approved GLP-1 pens.
Related profiles
- GLP-1 receptor agonist Semaglutide Semaglutide is a long-acting GLP-1 receptor agonist approved for type 2 diabetes, chronic weight management and cardiovascular risk reduction. Approved medicine
- Oral non-peptide ghrelin-receptor agonist MK-677 MK-677 (ibutamoren) is an orally active small molecule that mimics ghrelin and raises growth hormone and IGF-1. Human RCTs
- Non-selective melanocortin agonist Melanotan II Melanotan II is a synthetic cyclic peptide developed at the University of Arizona in the 1990s as a sunless tanning agent. Early human data
Questions
Are peptides safer than other drugs because they are natural?
No. Many peptides are potent hormones or hormone mimics. Safety depends on what the molecule does and how pure it is, not on whether a similar molecule exists in the body.
References
- Adunsky A, Chandler J, Heyden N, et al. (2011). MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Archives of Gerontology and Geriatrics.
- Kingsberg SA, Clayton AH, Portman D, et al. (2019). Bremelanotide for the Treatment of Hypoactive Sexual Desire Disorder: Two Randomized Phase 3 Trials. Obstetrics & Gynecology.
- Habbema L, Halk AB, Neumann M, Bergman W. (2017). Risks of unregulated use of alpha-melanocyte-stimulating hormone analogues: a review. International Journal of Dermatology.