A peptide is a short chain of amino acids, usually 2 to 50 amino acids long. Longer chains are called proteins. Your body already produces hundreds of peptides that act as signaling molecules: insulin (51 amino acids), oxytocin (9), glucagon (29), GLP-1 (30), and growth hormone-releasing hormone (44) are all peptides. Therapeutic peptides are manufactured copies of those natural signaling molecules, or modified analogs designed to last longer in the bloodstream, bind more selectively to a receptor, or reach a specific tissue. Because they mimic compounds the body already recognizes, peptides generally produce a more targeted effect and often a cleaner side-effect profile than small-molecule drugs. More than 80 peptide drugs are FDA-approved worldwide, and 170+ are in active clinical development.

Three distinct regulatory buckets exist in 2026, and understanding which bucket a peptide is in is the single most important thing a patient can know. Bucket 1 contains FDA-approved drugs that have gone through the full New Drug Application process with Phase 1 through 3 trials: semaglutide, tirzepatide, tesamorelin, bremelanotide, teduglutide, elamipretide, and octreotide. Bucket 2 contains 503A-compoundable peptides on the Category 1 list — not FDA-approved, but a licensed physician can legally prescribe them and a compounding pharmacy can prepare them for an individual patient. Bucket 3 contains research chemicals not legally available for human use, like FOXO4-DRI and novel senolytic peptides sold online labeled "research use only." The key distinction: "My doctor prescribed it and a compounding pharmacy made it" is not the same as "the FDA approved this drug."

On February 27, 2026, HHS Secretary Robert F. Kennedy Jr. announced that approximately 14 of the 19 peptides previously in Category 2 would be moved back to Category 1, allowing 503A pharmacies to compound them under patient-specific prescription. The reclassified peptides include AOD-9604, BPC-157, CJC-1295 (with or without DAC), emideltide (DSIP), epitalon, GHK-Cu, ipamorelin, kisspeptin-10, KPV, MOTS-c, selank, semax, TB-500 (thymosin beta-4 fragment), and thymosin alpha-1. Category 1 status is not FDA approval — it means the FDA has not identified overriding safety concerns that would prohibit compounding while the substance remains under ongoing evaluation. Expect wide variation in quality between compounding pharmacies.

BPC-157 is a synthetic 15-amino-acid fragment derived from a protective protein naturally produced in human gastric juice. A large body of rodent data shows improved tendon-to-bone healing, muscle repair, neuroprotection, and gastrointestinal cytoprotection. However, human clinical evidence remains limited to small case series and one retrospective study of 12 knee-pain patients; a Phase 1 safety trial was withdrawn in 2016 without publishing results. Typical clinical use is 250–500 mcg subcutaneously daily for 3 months on, 1 month off. Oral capsules at 500 mcg/day are used for gut indications because BPC-157 is stable in gastric acid. Approximate 2026 cost: $115/month injectable, $3/capsule oral. Patients with active or recent cancer should avoid it due to concerns about angiogenic effects.

CJC-1295 is a GHRH analog and ipamorelin is a selective GH secretagogue (ghrelin-receptor agonist). Together they produce a physiologic, pulsatile release of growth hormone rather than the supraphysiologic spikes seen with exogenous HGH. Short-term Phase 1/2 trials in healthy adults showed dose-dependent increases in GH and IGF-1 without clinically significant hyperglycemia. No long-term RCTs demonstrate improvement in mortality or biological age. Typical use is 100–200 mcg of each, subcutaneously nightly on an empty stomach, 5 nights on, 2 off, for 3 months then stop. IGF-1 should be monitored every 6–8 weeks. Anyone with active malignancy or pregnancy should avoid this stack. Approximate 2026 cost: $189/month combined.

Tesamorelin (Egrifta) is the only FDA-approved GHRH analog. It is a stabilized 44-amino-acid peptide resistant to DPP-4 degradation, giving it a much longer duration of action than sermorelin. FDA-approved in 2010 based on two pivotal Phase 3 RCTs demonstrating a 14–18% reduction in visceral adipose tissue at 26 weeks in HIV patients with lipodystrophy. The labeled dose is 2 mg subcutaneously daily. Off-label interest in non-HIV visceral obesity and NAFLD is supported by smaller mechanistic studies. Branded tesamorelin is expensive — often $3,000+/month cash pay without insurance. Sermorelin, a 29-amino-acid synthetic GHRH fragment that was FDA-approved in 1997 as Geref for pediatric growth hormone deficiency but voluntarily discontinued in 2008, is now available only as a 503A compound at approximately $135/month.

GHK-Cu is a tripeptide (glycyl-L-histidyl-L-lysine) bound to a copper ion, naturally present in human plasma with levels that fall sharply with age. It has robust in-vitro and dermatology evidence for wound healing, collagen and elastin synthesis, and hair follicle stimulation. It is a well-established cosmeceutical ingredient in topical formulations worldwide, though injectable systemic GHK-Cu has less rigorous human data. Epitalon is a synthetic tetrapeptide analog of the pineal peptide epithalamin. Several small Russian trials reported telomerase activation, melatonin normalization, and reduced all-cause mortality in elderly subjects over 6–12-year follow-ups, but these studies have not been independently replicated in Western populations. Both are now Category 1 at approximately $135/month.

The GLP-1 family — semaglutide, tirzepatide, liraglutide — are arguably the most consequential peptides in longevity medicine today, though the FDA has not approved any of them for anti-aging or longevity. The SELECT trial of approximately 17,600 participants demonstrated a 20% reduction in major adverse cardiovascular events with semaglutide in patients with obesity. SURMOUNT-1 showed approximately 22.5% mean weight loss at 72 weeks with tirzepatide 15 mg. Post-hoc epigenetic analysis of SELECT participants found semaglutide-treated patients showed a 1.4-year reduction in GrimAge acceleration independent of weight change. The FDA has issued specific warnings about compounded GLP-1 sodium and acetate products sold online, citing unapproved salt forms and dosing errors.

PT-141 (bremelanotide, brand name Vyleesi) is FDA-approved for premenopausal women with hypoactive sexual desire disorder based on two RECONNECT Phase 3 RCTs of over 1,200 women. Thymosin alpha-1 is approved in 30+ countries (not the US) as Zadaxin for hepatitis B, hepatitis C, and as an adjuvant in vaccines and cancer care, with randomized data in sepsis and COVID-19 being the most mature of any peptide on the Category 1 list. Kisspeptin-10 activates the hypothalamic-pituitary-gonadal axis upstream of GnRH, with Imperial College London having run multiple human RCTs showing it can safely stimulate endogenous LH, FSH, and testosterone in men with hypogonadism.

Starting peptide therapy safely requires a systematic approach. First, define a specific, measurable goal — recovery from injury, visceral fat reduction, sexual function, or immune support. Find a physician who monitors labs, not one who sells peptides from a retail counter. Baseline labs should include CBC, CMP, HbA1c, fasting insulin, IGF-1, testosterone, thyroid panel, hs-CRP, and PSA for men over 40. Screen out contraindications: active cancer, uncontrolled diabetes, pregnancy, unstable cardiovascular disease. Use only 503A compounding pharmacies with third-party certificates of analysis documenting USP-grade API source, endotoxin testing, sterility testing, and potency testing.

Start with one peptide at a time — stacking makes attribution of benefit and side effects impossible. Most peptides work best at 8–12 weeks on, 4 weeks off, which reduces receptor desensitization and flags accumulating side effects. Re-check labs at 8 weeks, then every 3 months. Stop immediately for rising HbA1c, IGF-1 above age-adjusted upper limit, new cardiac symptoms, or any new mass. The most common side effects across injectable peptides are injection-site reactions, transient flushing or headache, water retention with GH-axis peptides, and first-week fatigue with immune-modulating peptides. Universal red flags requiring immediate medical attention include severe abdominal pain, sudden visual changes, new or enlarging masses, and chest pain or shortness of breath.

No peptide has an FDA approval or a large RCT specifically for extending healthspan or lifespan in healthy adults. Most evidence comes from studies in patients with specific disease states. For metabolic health in obesity, GLP-1s have by far the best evidence. For sarcopenia and aging-related body composition decline, growth-hormone-secreting peptides have a reasonable mechanistic case. For injury recovery, BPC-157 combined with TB-500. For immune resilience after infection, thymosin alpha-1. The landscape has shifted dramatically in 2026 with the Category 1 reclassification, but patients should set realistic, measurable goals, use only licensed physicians and 503A pharmacies, and reassess at 8–12 weeks.