Origins, uses and approval
Their earlier biology helps explain the interest. Their tested uses determine how far the comparison can go.
Starting materials and studied uses
A plasma peptide, a melanocortin analogue and engineered gut-hormone medicines can all fit under the word “peptide.” Their histories lead in quite different directions. The original biological setting helps me tell these histories apart.
| Compound | Starting point and subsequent work |
|---|---|
| GHK-Cu | GHK was isolated from plasma through liver-tissue work; the copper-bound form has a largely topical skin-repair literature. See the skin-regeneration review. |
| PT-141 | A synthetic melanocortin relative became bremelanotide, with clinical trials in premenopausal women with HSDD. |
| Retatrutide | A single engineered peptide combines activity at GIP, GLP-1 and glucagon receptors; the obesity trial is Phase 2. |
| Semaglutide | A long-acting GLP-1 analogue moved from diabetes treatment into several other uses; SELECT measured cardiovascular events without diabetes. |
Human evidence and route
GHK-Cu has small topical studies plus cell and animal work. Its skin-penetration experiment used human skin outside the body. A dermal copper depot in that experiment supplies no human injection protocol.
Bremelanotide has two Phase 3 randomized trials in a defined HSDD population and a 52-week open-label extension. Retatrutide’s Phase 2 obesity results and diabetes results remain investigational. Semaglutide has large human trials including STEP 1, SELECT and FLOW, addressing different outcomes in different populations.
That unevenness makes a single league table unattractive to me. Hair count, sexual desire, body weight and major clinical events cannot be arranged into one meaningful scale of “peptide strength.”
Approval and safety
GHK-Cu has no FDA-approved drug indication; its established commercial use is as a topical cosmetic ingredient. Retatrutide remains an unapproved investigational compound. Bremelanotide’s approved HSDD indication is restricted to premenopausal women with acquired, generalized HSDD. Semaglutide’s approved uses include type 2 diabetes, chronic weight management, cardiovascular risk reduction in the specified population and MASH.
The cautions are equally specific. Bremelanotide’s label includes transient blood-pressure increases and contraindications in uncontrolled hypertension or cardiovascular disease. The retatrutide obesity trial recorded a dose-dependent heart-rate increase. The semaglutide safety review describes gastrointestinal intolerance, biliary disease and the thyroid-tumour warning derived from rodents. Human systemic GHK-Cu safety remains poorly established.
I see a great deal of invention in this group. Moving a result into a new route, product, population or combination requires additional work. The GHK-Cu with retatrutide FAQ applies that question to a pairing people search for.