Four Peptides, Four Different Evidence Stages

The short version

This page lines up BPC-157, NAD+, PT-141, and GHK-Cu on the dimensions that matter most for reading research-peptide literature: what kind of molecule each is, what it is mostly studied for, how mature the human evidence is, and its current regulatory status. The headline finding is that these four compounds are not interchangeable examples of one category — they sit at genuinely different points on the evidence spectrum, from a compound with a full FDA approval and label, to one whose human evidence is still three pilot reports. Nothing here is medical advice, and no dose is recommended for any compound on any row.

The comparison matrix

Molecule class

The four compounds are chemically unrelated apart from being short peptides or peptide-adjacent molecules. BPC-157 is a 15-amino-acid fragment derived from a gastric protective protein, notably stable against enzymatic breakdown ^[3]. NAD+ is technically a dinucleotide coenzyme rather than a peptide at all, though its precursors NMN and nicotinamide riboside are grouped into the same research-peptide category by convention ^[9]. PT-141 (bremelanotide) is a seven-amino-acid cyclic peptide engineered as an analogue of a natural pituitary hormone, alpha-MSH ^[15]. GHK-Cu is the smallest of the four — a three-amino-acid tripeptide bound to a copper ion, occurring naturally in the body as a byproduct of collagen turnover ^[19]. Nothing about their shared "peptide" label implies a shared mechanism, shared safety profile, or shared regulatory category.

Most-studied application

Each compound has settled into a distinct research niche. BPC-157 is studied almost entirely for tissue repair and gut protection, driven by an angiogenesis mechanism demonstrated across animal and cell models ^[4][5]. NAD+ and its precursors are studied for cellular energy metabolism and the biology of aging, with the strongest data showing reliable elevation of blood NAD+ levels ^[7][10]. PT-141 has a single, tightly defined studied application: hypoactive sexual desire disorder in premenopausal women, backed by two large Phase 3 trials ^[13]. GHK-Cu's studied application is almost entirely topical dermatology — skin structure, wrinkle depth, and hair growth — rather than any systemic use ^[16][18][19]. Reading any of the four outside its actual studied niche means leaving the evidence behind.

Evidence maturity

This is where the four compounds separate most sharply. PT-141 has the most rigorous human evidence: randomized, placebo-controlled Phase 3 trials with over 1,200 participants and a year-long open-label safety extension, all feeding directly into an FDA approval ^[13][14][15]. GHK-Cu has the longest human track record by calendar time — dermatology and hair studies going back to 1988 — but concentrated in small trials (roughly a dozen to several dozen participants) rather than large outcome studies ^[16][18][22]. NAD+ precursor supplementation has solid, repeated controlled-trial evidence for one specific outcome (raising blood NAD+) but a considerably thinner record for whether that translates into a clinical benefit, as the 2025 review notes directly ^[6]. BPC-157 has the least mature human evidence of the four: as of 2025, only three small human pilot reports exist, and the compound is explicitly described in the literature as investigational ^[1][2].

Regulatory and access status

Only PT-141 (as bremelanotide) is an FDA-approved prescription medicine, and only for one indication in one population ^[15]. NAD+ and its precursors are sold as dietary supplements — a lower evidentiary bar than a drug approval — though NMN specifically faces a contested marketplace status because the FDA considers it to have been first investigated as a drug. GHK-Cu's status is split by route: topical Copper Tripeptide-1 is a legal, widely used cosmetic ingredient, while injectable or oral systemic GHK-Cu has no approved pathway. BPC-157 has no approved use anywhere and is sold exclusively as a research chemical for laboratory use. This split matters more than it might seem: it determines whether a given claim about a compound is describing an approved therapy, a lightly regulated supplement, a cosmetic ingredient, or an unregulated research chemical, and each of those carries a different evidentiary and safety standard.

Key caution

Each compound carries a defining caution worth holding onto. For BPC-157, it is the sheer thinness of the human evidence combined with theoretical, mechanism-based concerns about cancer and serotonin-medicine interactions drawn from animal data ^[2][4]. For NAD+, it is the gap between a well-demonstrated blood-marker effect and an unproven clinical-outcome effect, plus a documented contamination risk in compounded injectable products. For PT-141, it is that its real, rigorous evidence base covers a narrow population and indication — nausea affects roughly 40% of long-term users, and everything outside the approved use is unstudied by the same standard ^[13][14]. For GHK-Cu, it is that the entire validated human evidence base is topical; there is no validated human pharmacokinetic data for injectable or systemic use, and community injection protocols have no peer-reviewed basis. Read together, the pattern across all four is the same: evidence maturity is compound-specific, not category-wide, and "it's a research peptide" says almost nothing on its own about how well-studied a given claim actually is.