“Peptide” covers a very large family: short chains of amino acids that the body already makes, and many copies of them sold online. Most of what is sold is studied in cell cultures and animals. Only a handful have been tested in people in controlled trials, and most of those trials were about one disease, not about longevity. This article sets out what we could verify, and where the evidence ends.
Tesamorelin: the strongest human data
Tesamorelin is a synthetic analog of growth hormone releasing hormone (GHRH), the signal that tells the pituitary to release growth hormone. In a randomized trial of 412 adults with HIV and excess abdominal fat, daily tesamorelin 2 mg for 26 weeks reduced visceral fat by about 15%, while the placebo group gained about 5%. Subcutaneous fat in the limbs barely changed. This is the reason it is FDA-approved, and it is for that specific HIV-related condition.
Thymosin alpha-1: an older immune peptide
In a randomized trial of 98 adults with chronic hepatitis B, 26 weeks of thymosin alpha-1 gave a complete virological response in 40.6% of patients at 18 months, against 9.4% of untreated controls. The drug is used for hepatitis B in several countries outside the United States; it is not FDA-approved for that use. Its sales claims for immunity or longevity are not supported by the trial above.
Growth hormone releasing hormone and cognition
In a randomized, double-blind trial of 152 adults aged 55 to 87, daily tesamorelin for 20 weeks improved executive function compared with placebo (P = .005), in both healthy older adults and adults with mild cognitive impairment. The authors describe the result as preliminary and call for larger, longer trials.
Sermorelin and older growth hormone secretagogues
Sermorelin is another GHRH analog. It was an FDA-approved product, and it was later withdrawn by its manufacturer. A 2006 editorial in Clinical Interventions in Aging argued that it offers a more physiological alternative to injected growth hormone. That article is an opinion piece with limited data; we did not find a long-term trial showing that sermorelin improves outcomes compared with growth hormone.
GHK-Cu, and the rest of the list
GHK-Cu, the copper peptide used in skin products and injections, has strong data from cell and tissue studies on collagen and wound repair. The human studies we found are small, often unpublished in full, and linked to product sellers, so we do not quote their numbers. For most other peptides on the market, including KPV, MOTS-c, epithalon, LL-37, Semax and Selank, we found no published human outcome trial that we could verify.
The regulatory picture
In August 2026 the FDA sent five warning letters to online sellers of peptides labeled “research use only”, concluding from their websites that the products were unapproved drugs. Under the 503A bulk substances list, FDA has placed several peptides in categories that restrict compounding, and that list has changed over time. Status should be checked on fda.gov at the time of any decision, not taken from a summary.
What this does not say
- The trials above used the studied medicines at the studied doses, mostly brand or reference products. Compounded peptides were not tested in them.
- Trial averages are not predictions for one person. Each trial enrolled a specific group and measured a specific outcome.
- Tesamorelin is approved for HIV-related abdominal fat. Its other uses are not approved, and its effects on longevity have not been tested.
- Safety data for most peptides on the market are short or missing. Injection-site reactions, fluid retention and higher blood glucose have been reported with growth hormone-stimulating drugs.
How we use this
We recommend a peptide only when there is human data that fits the reason for prescribing it, and when a physician has reviewed your history. Where the evidence is animal or cell data alone, we say so, and we do not present it as a treatment result.
The rest of the online market works the other way around: a bold claim comes first and the data, if any, come later. Our physicians start with the data and the limits, then talk to you about what fits.
Explore weight loss treatmentsSources
- 1.Falutz J et al. Effects of tesamorelin (TH9507), a growth hormone-releasing factor analogue, in HIV-infected patients with excess abdominal fat. N Engl J Med 2007. NEJM
- 2.Chien RN et al. Efficacy of thymosin alpha 1 in patients with chronic hepatitis B: a randomized, controlled trial. Hepatology 1998;27:1383-1387. Hepatology
- 3.Baker LD et al. Effects of growth hormone-releasing hormone on cognitive function in adults with mild cognitive impairment and healthy older adults: results of a controlled trial. Arch Neurol 2012;69(11):1420-1429. Archives of Neurology
- 4.Walker RF. Sermorelin: a better approach to management of adult-onset growth hormone insufficiency? Clin Interv Aging 2006;1(4):307-308. Clinical Interventions in Aging
- 5.Vasireddi N et al. Emerging use of BPC-157 in orthopaedic sports medicine: a systematic review. HSS J 2025;21(4):485-495. HSS Journal