Peptide therapy: promise, pitfalls and what patients should know

What exactly is “peptide therapy”?

Peptide therapy is a medical treatment that utilizes specific peptides—short chains of amino acids—to promote healing, enhance physical performance, and improve overall health.

Peptides are short chains of amino acids—typically 2–50 residues—small enough to act like highly targeted biological “messages” but large enough to be very specific for a receptor or enzyme. In the last few decades, peptides have emerged as one of the most active areas in drug development. More than 80 peptide drugs are already approved worldwide, including insulin, GLP-1 receptor agonists for diabetes and obesity, vasopressin analogues for shock, and linaclotide for irritable bowel syndrome. Nature+2MDPI+2

When people talk about “peptide therapy” in clinics and on social media, they often mean both these well-validated, regulator-approved peptide drugs and a growing assortment of compounded or “research” peptides marketed for fat loss, musculoskeletal repair, sexual function, brain health and skin rejuvenation. The spectrum runs from mainstream endocrinology and oncology to experimental, poorly regulated products ordered online.

Understanding where a given peptide sits on that spectrum—established, emerging, or speculative—is the first step in having an intelligent conversation about benefits and risks.

Why are peptides attractive as therapeutics?

From a pharmacologic standpoint, peptides occupy a kind of sweet spot between small molecules and full-length proteins or antibodies:

• High specificity. Peptides can mimic physiological hormones or binding motifs and often act on a single receptor or pathway, which can reduce off-target effects. Nature+1

• Potent signaling. Many endocrine and neuroendocrine axes are peptide-driven; replacing or modulating those signals can be very powerful.

• Predictable metabolism. Peptides are generally broken down into amino acids or small fragments, rather than accumulating as long-lived xenobiotics.

• Design flexibility. Advances in solid-phase synthesis, peptide “stapling,” cyclization, PEGylation and depot formulations have greatly improved half-life, stability and route of administration. MDPI+1

  
  

The flip side is that peptides are often labile in the GI tract, leading to a predominance of injectable products, although oral peptide drugs such as oral semaglutide and linaclotide show that this barrier can be overcome. Nature+2Nature+2

Well-established peptide therapies

A few examples illustrate how deeply peptide therapy is already embedded in standard care:

• Insulin and insulin analogues. The first therapeutic peptide and still a cornerstone of diabetes management. Modified insulins manipulate absorption, aggregation and receptor kinetics to produce ultra-rapid or ultra-long action profiles. Nature

• GLP-1 receptor agonists (e.g., exenatide, liraglutide, semaglutide). Originally approved for type 2 diabetes, GLP-1 RAs are now central to evidence-based obesity treatment, with large randomized trials showing significant weight loss and improved glycemic control. New England Journal of Medicine+2PMC+2

• Other gut peptides (e.g., linaclotide). Linaclotide is a 14–amino acid peptide agonist of guanylate cyclase-C used for IBS-C and chronic idiopathic constipation, with multiple phase 3 trials supporting efficacy and safety. Nature+2PubMed+2

• Peptide receptor radionuclide therapy (PRRT). Somatostatin-analog peptides coupled to radionuclides are now standard in many centers for imaging and treating neuroendocrine tumors. Nature

  
  

These drugs have gone through the full regulatory process: dose-finding, randomized controlled trials, post-marketing surveillance and, crucially, manufacturing under strict quality control.

The “new frontier”: emerging and boutique peptide therapies

Where things become more heterogeneous is in the world of emerging or “boutique” peptide therapy, much of it delivered in cash-pay clinics or via online vendors. A few classes are especially prominent:

1. Growth hormone secretagogues (GHSs) and GHRH analogues

Agents such as GHRH analogues and ghrelin receptor agonists (e.g., tesamorelin, macimorelin, ipamorelin and related molecules) stimulate endogenous GH release rather than providing recombinant GH itself. A 2020 review details their mechanisms, pharmacology and clinical trials in indications ranging from GH deficiency diagnosis to visceral adiposity and GI dysmotility. Wiley Online Library+1

Some, like tesamorelin, have formal approvals (HIV-associated lipodystrophy); others are studied but not widely licensed. As age-management and sports-medicine markets have embraced “peptide stacks,” the clinical use of GHSs has outpaced high-quality long-term safety data in otherwise healthy adults.

2. Regenerative and musculoskeletal peptides: BPC-157 and others

BPC-157, a gastric pentadecapeptide, has attracted intense interest for tendon, ligament, bone and muscle healing. Preclinical models consistently show enhanced angiogenesis, fibroblast migration, and biomechanical strength at injury sites. PMC+1

However, a 2025 systematic review in HSS Journal found 35 preclinical studies but only a single small retrospective human series (12 patients). There is no FDA-approved indication, and major sports organizations and the World Anti-Doping Agency have banned BPC-157 or categorized it as a prohibited peptide hormone. PMC+2PMC+2

The authors conclude that while laboratory results are intriguing, human safety is unknown, and unregulated compounding introduces risks of contamination, mislabeling and dose inconsistency.

3. Tanning and sexual-function peptides: Melanotan II and derivatives

Melanotan II is an analog of α-melanocyte–stimulating hormone developed decades ago to induce tanning; it also has potent effects on appetite and sexual function. It was never approved as a cosmetic but gave rise to bremelanotide, an FDA-approved peptide for hypoactive sexual desire disorder. DermNet®+1

Nonetheless, Melanotan II itself has become widespread in the form of black-market injections and nasal sprays marketed for rapid tanning and libido. Case reports and reviews describe:

• Rapid darkening of moles, eruptive nevi and cases of melanoma temporally associated with Melanotan II use, often in the setting of intense UV exposure. PMC+2OUP Academic+2

• Short-term adverse effects such as nausea, vomiting, flushing and priapism. DermNet®+2UNSW Sites+2

  
  

Regulators in multiple countries have explicitly warned consumers against these products, stressing that they are unlicensed, untested and potentially carcinogenic. Courier Mail+3UNSW Sites+3Therapeutic Goods Administration (TGA)+3

Evidence, regulation and the problem of “research peptides”

The key distinction patients rarely see in marketing copy is this:

Many peptides being sold online or in off-label protocols are not approved drugs; they are experimental compounds, frequently labeled “for research use only.”

The FDA and other regulators have taken specific actions against compounding certain peptides (including BPC-157) as bulk substances because of insufficient safety data and potential for harm. PMC+1

From an evidence-based standpoint:

• Approved peptide drugs – have robust clinical trial data, known adverse-event profiles, pharmacokinetics, standardized dosing and manufacturing oversight.

• Investigational peptides in formal trials – may be promising, but access should be via controlled studies with ethics oversight and monitoring.

• Unregulated, “gray-market” peptides – often lack dose-response data, long-term safety information, and quality control. Analytical surveys of “ergo-nutritional” supplements suggest contamination rates between 12% and 58%, including undeclared drugs. https://pmc.ncbi.nlm.nih.gov/articles/PMC12313605/

Clinically, that means two patients “on BPC-157” or “on a peptide stack” may be receiving completely different molecules and doses, with unpredictable risk.

How are peptide therapies administered?

Most peptide therapies are given by subcutaneous injection, but there is considerable innovation in delivery:

• Depot formulations (e.g., weekly GLP-1 analogues) extend half-life and improve adherence. PubMed+2Taylor & Francis Online+2

• Oral formulations using permeability enhancers and protective carriers have brought oral semaglutide and other peptide drugs to market, and additional oral peptides are in late-stage development. Nature+1

• Transmucosal and transdermal systems are being explored, but most remain experimental. Nature

  
  

Route of administration is not merely a convenience issue; it has implications for immunogenicity, peak-trough variability, and patient ability to self-manage therapy safely.

Benefits patients may reasonably expect

Where high-quality data exist, peptide therapies can deliver substantial benefit:

• Metabolic health and weight management. GLP-1 receptor agonists and related incretin-based peptides reduce HbA1c, body weight and certain cardiovascular risk markers in appropriate patients, especially when combined with nutrition and activity interventions. New England Journal of Medicine+2JAMA Network+2

• GI motility and pain. Linaclotide and related peptides improve bowel habits and abdominal pain in IBS-C and chronic constipation. PubMed+2PubMed+2

• Cancer, hematology and rare diseases. A growing portfolio of peptide-drug conjugates, peptide radionuclide therapies and targeted peptide antagonists is in late-stage trials and clinical use, particularly in oncology and rare endocrine disorders. Nature+1

  
  

By contrast, for many of the “performance,” “longevity,” or anti-aging peptides promoted online, the evidence is limited to animal studies, small uncontrolled human series, or extrapolation from related molecules. That doesn’t make them useless, but it does mean expectations should be modest, and consent conversations explicit about uncertainty.

Risks, side effects and practical cautions

Across peptide classes, the main risk domains are:

• Pharmacologic side effects. Hypoglycemia with insulin or insulin secretagogues; GI upset, gallbladder disease and rare pancreatitis with GLP-1 RAs; injection-site reactions; changes in melanocytic lesions with Melanotan II; fluid shifts or carpal-tunnel–like symptoms with aggressive GH axis stimulation. Wiley Online Library+3PMC+3PubMed+3

• Immunogenicity and hypersensitivity. Any peptide can theoretically provoke an immune response; true anaphylaxis is uncommon but documented with several biologic agents.

• Quality and contamination. Perhaps the most underappreciated risk. Analyses of internet-purchased “research peptides” have found incorrect identity, incorrect dose, bacterial contamination and undeclared excipients.

• Regulatory/ethical issues. Athletes may be in violation of anti-doping codes; clinicians may run afoul of compounding regulations or state medical boards if using non-approved bulk substances. Therapeutic Goods Administration (TGA)+3PMC+3Wikipedia+3

  
  

For patients, the practical questions to ask are:

1. Is this peptide an approved drug for my indication, or is it experimental?

2. What human data exist—randomized trials, observational series, or only preclinical work?

3. How is the product sourced and quality-controlled?

4. How will side effects be monitored and managed over time?

   
   

These are the questions that separate thoughtful, patient-centered peptide therapy from opportunistic marketing.

The future of peptide therapy

Recent bibliometric analyses show an exponential rise in peptide-related publications, patents and market size, with the global peptide therapeutics market projected to continue double-digit annual growth. MDPI+1

Areas likely to expand over the coming decade include:

• Multi-agonist metabolic peptides combining GLP-1, GIP, glucagon or amylin activities for obesity, NASH and cardiometabolic disease.

• Tumor-targeted peptide–drug conjugates and vaccines.

• Anti-infective and antiviral peptides, including those targeting coronavirus fusion mechanisms. Nature+1

  
  

If development continues along its current trajectory, patients will see more peptide drugs, not fewer—many of them with sophisticated delivery systems and highly specific indications.

The challenge for clinicians and patients is to distinguish between peptides whose benefits and risks are well-characterized and those that are still, in truth, experimental agents being marketed as finished therapies.

References

1. Wang L, Wang N, Zhang W, et al. Therapeutic peptides: current applications and future directions. Signal Transduct Target Ther. 2022;7(1):48. doi:10.1038/s41392-022-00904-4. Available at: https://www.nature.com/articles/s41392-022-00904-4 Nature

2. Xiao W, Jiang W, Chen Z, et al. Advance in peptide-based drug development: delivery platforms, therapeutics and vaccines. Signal Transduct Target Ther. 2025;10:74. doi:10.1038/s41392-024-02107-5. Available at: https://www.nature.com/articles/s41392-024-02107-5 Nature

3. Rossino G, Marchese E, Galli G, et al. Peptides as therapeutic agents: challenges and opportunities in the green transition era. Molecules. 2023;28(20):7165. doi:10.3390/molecules28207165. Available at: https://www.mdpi.com/1420-3049/28/20/7165 MDPI

4. Fosgerau K, Hoffmann T. Peptide therapeutics: current status and future directions. Drug Discov Today. 2015;20(1):122-128. doi:10.1016/j.drudis.2014.10.003. Available at: https://pubmed.ncbi.nlm.nih.gov/25450771/ PubMed

5. Lau JL, Dunn MK. Therapeutic peptides: historical perspectives, current development trends, and future directions. Bioorg Med Chem. 2018;26(10):2700-2707. doi:10.1016/j.bmc.2017.06.052. Available at: https://pubmed.ncbi.nlm.nih.gov/28720446/ Nature

6. Muttenthaler M, King GF, Adams DJ, Alewood PF. Trends in peptide drug discovery. Nat Rev Drug Discov. 2021;20(4):309-325. doi:10.1038/s41573-020-00135-8. Available at: https://pubmed.ncbi.nlm.nih.gov/32901188/ Nature

7. Pi-Sunyer X, Astrup A, Fujioka K, et al. A randomized, controlled trial of 3.0 mg of liraglutide in weight management. N Engl J Med. 2015;373(1):11-22. doi:10.1056/NEJMoa1411892. Available at: https://www.nejm.org/doi/full/10.1056/NEJMoa1411892 New England Journal of Medicine+1

8. Ladenheim EE. Liraglutide and obesity: a review of the data so far. Drug Des Devel Ther. 2015;9:1867-1875. doi:10.2147/DDDT.S67400. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC4386791/ PMC+1

9. Knop FK, Bronden A, Lauritsen TV. Exenatide: pharmacokinetics, clinical use, and future directions. Expert Opin Pharmacother. 2017;18(6):555-571. doi:10.1080/14656566.2017.1282463. Available at: https://www.tandfonline.com/doi/full/10.1080/14656566.2017.1282463 PubMed+1

10. Lembo AJ, Schneier HA, Shiff SJ, et al. Two randomized trials of linaclotide for chronic constipation. N Engl J Med. 2011;365(6):527-536. doi:10.1056/NEJMoa1010863. Available at: https://www.nejm.org/doi/full/10.1056/NEJMoa1010863 New England Journal of Medicine

11. Chey WD, Lembo AJ, Lavins BJ, et al. Linaclotide for irritable bowel syndrome with constipation: a 26-week, randomized, double-blind, placebo-controlled trial. Clin Gastroenterol Hepatol. 2012;10(8):741-749.e1. doi:10.1016/j.cgh.2012.05.016. Available at: https://pubmed.ncbi.nlm.nih.gov/22986437/ PubMed

12. Menda Y, Madsen MT, O’Dorisio TM, et al. 90Y-DOTATOC dosimetry-based personalized peptide receptor radionuclide therapy. J Nucl Med. 2018;59(11):1692-1698. doi:10.2967/jnumed.118.210658. Available at: https://pubmed.ncbi.nlm.nih.gov/29871864/ Nature

13. Ishida J, Saitoh M, Ebner N, et al. Growth hormone secretagogues: history, mechanism of action, and clinical development. JCSM Rapid Commun. 2020;3(1):25-37. doi:10.1002/rco2.9. Available at: https://onlinelibrary.wiley.com/doi/10.1002/rco2.9 Wiley Online Library+1

14. Vasireddi N, Hahamyan H, Salata MJ, et al. Emerging use of BPC-157 in orthopaedic sports medicine: a systematic review. HSS J. 2025;21(4):1-11. doi:10.1177/15563316251355551. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC12313605/ PMC+1

15. Brcic I, Brcic L, Staresinic M, et al. Modulatory effect of gastric pentadecapeptide BPC 157 on angiogenesis in muscle and tendon healing. J Physiol Pharmacol. 2009;60(Suppl 7):191-196. Available at: https://pubmed.ncbi.nlm.nih.gov/20388945/ Sports Medicine Review

16. Sivyer GW, Muir JB, Evans AV, David M. Changes of melanocytic lesions induced by Melanotan-2. Australas J Dermatol. 2012;53(2):123-127. doi:10.1111/j.1440-0960.2011.00866.x. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC3663356/ PMC

17. Hjuler KF, Gniadecki R. Melanoma associated with the use of melanotan-II. Dermatol Ther (Heidelb). 2014;4(1):135-138. doi:10.1007/s13555-014-0046-1. Available at: https://pubmed.ncbi.nlm.nih.gov/24355990/ PubMed

18. Brennan R, Wells JS, Van Hout MC. An unhealthy glow? A review of melanotan use and harm. Eur J Integr Med. 2014;6(6):637-647. doi:10.1016/j.eujim.2014.04.002. Available at: https://www.sciencedirect.com/science/article/pii/S2211266915000055 ScienceDirect

19. DermNet NZ. Melanotan II. Updated 2023. Available at: https://dermnetnz.org/topics/melanotan-ii DermNet®

20. World Anti-Doping Agency (WADA). Prohibited List 2025. Substances and methods prohibited at all times. Includes peptide hormones and their analogues (e.g., BPC-157, Melanotan II). Available at: https://www.wada-ama.org/en/resources/world-anti-doping-program/prohibited-list Wikipedia+1

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