Peptide Therapies Explained: What They Are, How They Work, and What's Actually Proven

The Short Answer

Peptides are short chains of amino acids — small proteins, essentially — that act as signaling molecules in the body. Some peptide drugs are among the most rigorously proven medications in existence (insulin was the first therapeutic peptide, introduced in the 1920s). Others sold at wellness clinics have little or no human evidence behind them.

One important note before we go further: GLP-1 weight-loss medications like semaglutide and tirzepatide are peptides too — arguably the most successful peptide drugs ever made. We cover them separately in Weight Loss Medications Explained and our GLP-1 Price Guide. This guide covers the peptides you'll encounter at longevity and wellness clinics — growth hormone secretagogues, healing peptides, and others — plus a few non-peptide therapies sold alongside them, like NAD+.

The honest summary: a handful are FDA-approved for specific uses, several are promising but under-studied, and some are popular despite almost no human data. Here's how to tell which is which.

What Peptides Actually Are

A peptide is a chain of amino acids — usually between 2 and 50 of them. Longer chains are called proteins. Because peptides are small and structurally similar to the body's own signaling molecules, they can bind to specific receptors and trigger specific responses: release a hormone, dilate a blood vessel, modulate inflammation.

That specificity is why drug companies love them. Insulin, GLP-1 agonists, and oxytocin are all peptides. It's also why wellness clinics love them: "targeted signaling molecule" sounds precise and scientific. Sometimes it is. Sometimes the target has only been demonstrated in rodents.

Growth Hormone Secretagogues

What they are: Peptides that stimulate your pituitary gland to release more of your own growth hormone, rather than injecting growth hormone directly. The common ones are sermorelin, ipamorelin, CJC-1295, and tesamorelin.

Claimed benefits: Improved body composition, better sleep, faster recovery, reduced belly fat, "anti-aging."

Evidence level: Mixed, and it matters which one. Tesamorelin is FDA-approved — but for a specific indication: reducing excess abdominal fat in people with HIV-associated lipodystrophy. Its use for general body composition is off-label. Sermorelin was previously FDA-approved as a diagnostic and pediatric therapy; it's now available mainly through compounding pharmacies. Ipamorelin and CJC-1295 have never been FDA-approved for anything — the human data consists mostly of small, short studies showing they raise growth hormone levels, not that they improve outcomes people care about.

Common side effects: Injection-site reactions, water retention, joint aches, increased hunger, tingling. Raising growth hormone also raises IGF-1, and the long-term safety of doing that in healthy adults is genuinely unknown.

Healing and Recovery Peptides: BPC-157 and TB-500

What they are: BPC-157 is a synthetic peptide derived from a protein found in gastric juice. TB-500 is a synthetic version of a fragment of thymosin beta-4. Both are marketed for tendon, ligament, muscle, and gut healing.

Claimed benefits: Faster injury recovery, reduced inflammation, gut repair.

Evidence level: This is where honesty matters most. The animal data — mostly rodent studies — is genuinely intriguing. The human data is thin to nearly nonexistent. There are no large published randomized controlled trials of BPC-157 or TB-500 in humans. The FDA has placed BPC-157 in a category of substances that raise significant safety risks for compounding, and neither peptide is approved for human use. WADA bans both in sport.

Common side effects: Largely unknown at a rigorous level, which is itself the point — nausea, dizziness, and injection-site reactions are reported anecdotally, but there's no systematic human safety data.

NAD+ (Precursors and Injections)

What it is: NAD+ is a coenzyme involved in cellular energy production; levels decline with age. Clinics offer it as IV infusions or injections, and supplement makers sell precursors (NMN, NR) that your body converts into NAD+.

Claimed benefits: Energy, cognitive clarity, cellular repair, longevity.

Evidence level: Precursors like NR reliably raise NAD+ blood levels in humans — that part is proven. What hasn't been demonstrated is that raising NAD+ levels translates into meaningful health outcomes in humans. Trials to date have been small and results modest. IV NAD+ has even less controlled evidence behind it than the oral precursors. Promising biology, unproven benefit. (More on NMN and NR in our longevity supplements guide.)

Common side effects: Oral precursors are generally well tolerated (flushing, nausea). IV infusions commonly cause chest tightness, cramping, and nausea if run quickly.

Sexual Health: PT-141 (Bremelanotide)

What it is: A melanocortin-receptor agonist that acts on the nervous system rather than blood flow — a genuinely different mechanism from Viagra-type drugs.

Claimed benefits: Increased sexual desire and arousal.

Evidence level: This one is legitimate: bremelanotide is FDA-approved as Vyleesi for acquired, generalized hypoactive sexual desire disorder in premenopausal women. Use in men, or for general "libido enhancement," is off-label with weaker evidence.

Common side effects: Nausea (common — affects a large share of users), flushing, headache, and temporary blood pressure increases. Not for people with uncontrolled hypertension or cardiovascular disease.

Skin and Other: GHK-Cu

What it is: A copper-binding peptide found naturally in human plasma, used in topical serums, microneedling, and sometimes injections.

Claimed benefits: Skin firmness, wrinkle reduction, wound healing, hair growth.

Evidence level: Reasonable evidence for topical cosmetic use — several small studies show improvements in skin appearance. Injectable and systemic use is far less studied. Not FDA-approved as a drug; in cosmetics it's regulated as an ingredient, not a treatment.

Common side effects: Topically, occasional irritation. Injectable use carries the usual unknowns of an unapproved compound.

The Evidence Spectrum at a Glance

The Regulatory Reality (Read This Before You Buy)

Most clinic peptides exist in a gray zone. They're not FDA-approved drugs, so they reach patients through compounding pharmacies — facilities that can legally prepare customized medications under a prescription. The FDA has been tightening which peptides compounders may use, and has flagged several (including BPC-157) as raising safety concerns for compounding. Availability of specific peptides shifts as this evolves.

Why sourcing matters — and this is a real safety point, not a scare tactic: peptides sold by gray-market "research chemical" websites are not manufactured for human use. Independent testing of such products has repeatedly found purity problems, inaccurate dosing, and contamination. An injected product with no pharmacy oversight is a genuinely different risk than the same molecule from a licensed compounding pharmacy operating under a physician's prescription. If you're going to use peptides at all, use a licensed clinic with a real prescribing physician and a named pharmacy — never a site that ships vials labeled "not for human consumption."

Where to Go From Here

If you're weighing whether peptide therapy is worth the money, start with Peptide Therapy: What It Is, What It Costs for typical pricing. If you've decided to move forward and want a vetted, physician-supervised option, see our comparison of the best peptide telehealth providers.

*This guide is for information only and is not medical advice. Talk to a licensed clinician before starting or changing any treatment or supplement.*