Research · 9 min read · Published September 8, 2026

Peptides for Hair Growth: GHK-Cu, PTD-DBM and the PP405 Phase 2a Results

What the evidence tiers actually are for the hair-growth peptides sold online: GHK-Cu (animal and cosmetic data), AHK-Cu (in vitro only), PTD-DBM (one 2017 mouse study), and PP405, the topical small molecule whose Phase 2a trial reported 31 percent of men gaining more than 20 percent hair density at 8 weeks, set against 48-week minoxidil and 1-year finasteride trials.

Do peptides regrow hair?

Not in any controlled human trial published as of September 2026. GHK-Cu has animal and in vitro data, AHK-Cu one in vitro study, PTD-DBM one 2017 mouse study. The strongest human result belongs to PP405, a small molecule, not a peptide: in its 78-person Phase 2a, 31 percent of men gained over 20 percent density at 8 weeks, placebo 0.

Regulatory status first. No peptide is approved for androgenetic alopecia by the FDA or any other regulator. GHK-Cu and AHK-Cu are sold as cosmetic ingredients in serums and shampoos, a category that requires no efficacy evidence. PTD-DBM is a research peptide with no investigational new drug application and no human study. PP405 is an investigational drug in a company-run development program, not available outside trials. The two approved options remain topical minoxidil (over the counter) and oral finasteride (prescription), and this article uses their trial numbers as the ruler against which every peptide claim is measured.

What the approved treatments actually deliver

It is hard to judge a hair claim without a baseline, so here is the baseline. In the pivotal 48-week trial of 393 men aged 18 to 49, 5 percent minoxidil solution twice daily increased non-vellus hair count by 18.6 hairs per square centimeter, 2 percent minoxidil by 12.7 and placebo by 3.9, with more itching and irritation at the higher strength (JAAD, 2002). In two 1-year trials of 1,553 men aged 18 to 41 with vertex loss, finasteride 1 mg daily increased hair count in a 1-inch circle by 107 hairs relative to placebo at one year and 138 at two years, from a baseline of 876, while placebo-treated men kept losing hair (JAAD, 1998). Both are human RCTs with hundreds to thousands of participants, objective hair counts and a year or more of follow-up. No peptide study comes close on any of those three dimensions.

What is the evidence for GHK-Cu and hair?

GHK-Cu's hair-growth evidence is animal and in vitro. The most-cited study is a 1993 Journal of Investigative Dermatology paper in which a copper-binding peptide applied to fuzzy rats enlarged vellus follicles 'similar to that of topical minoxidil'. Reviews list hair growth as a GHK-Cu effect without citing a controlled human trial, and none exists in the peer-reviewed literature.

GHK-Cu is the best-studied copper peptide for skin, with wound-healing and collagen data going back to the 1970s, and that reputation gets transferred to hair without the same evidence. Hideo Uno's macaque and rat work, reported in JID in 1993, is the origin of the claim: a copper-binding peptide (coded PC1031) applied to the back skin of fuzzy rats enlarged the vellus follicles, and the authors compared the effect to topical minoxidil in the same model. That is a rodent skin experiment from three decades ago. Loren Pickart's 2018 review of GHK-Cu's gene-level actions, which is otherwise detailed, states that the peptide can 'increase hair growth and thickness, enlarge hair follicle size' as a bullet point without a supporting human citation (PMC, 2018). Vendor sites cite small human comparisons against minoxidil, but we could not locate them in PubMed and do not count them. Evidence tier for hair: animal and in vitro.

AHK-Cu: one in vitro study

AHK-Cu is marketed as the hair-specific copper peptide, and its entire published basis is a 2007 study in Archives of Pharmacal Research. Pyo and colleagues exposed human hair follicles ex vivo and cultured dermal papilla cells to AHK-Cu at concentrations from 10^-12 to 10^-9 molar and observed follicle elongation and dermal papilla proliferation; a reduction in dermal papilla apoptosis did not reach significance (Arch Pharm Res, 2007). Human follicles in a dish are a legitimate screening model and nothing more: they say nothing about whether the peptide penetrates scalp, reaches the follicle at that concentration, or changes hair count on a head. Evidence tier: in vitro, one study, no replication.

What did the PTD-DBM mouse study show?

In a 2017 Journal of Investigative Dermatology paper, Lee and colleagues at Yonsei University identified CXXC5 as a brake on Wnt/beta-catenin signaling that was elevated in miniaturized follicles from balding human scalps. A peptide (PTD-DBM) that blocks CXXC5 from binding Dishevelled accelerated hair regrowth in mice and, combined with valproic acid, induced new follicles in wounds. No human study followed.

This is the most interesting mechanism in the peptide group, which is why it should be described precisely. The paper showed that mice lacking CXXC5 regrew hair faster, that valproic acid (a Wnt activator) amplified that, and that the competing peptide reproduced the effect in normal mice and promoted wound-induced hair neogenesis when co-applied with valproic acid. The human element is limited to tissue: CXXC5 was elevated in miniaturized follicles and arrector pili muscles of balding human scalp, which supports the target, not the treatment. In the nine years since, no clinical trial of PTD-DBM has been registered or published. Products sold under the name are research peptides of unverified identity; our certificate of analysis guide explains why that matters. Evidence tier: animal.

What did the PP405 Phase 2a trial find?

Pelage reported on June 17, 2025 that in a randomized, placebo-controlled Phase 2a of 78 men and women with androgenetic alopecia who applied PP405 or placebo once daily for 4 weeks, 31 percent of treated men with more advanced loss had over 20 percent higher hair density at week 8, placebo 0, with no systemic absorption. Phase 3: planned 2026.

PP405 is not a peptide. It is a topical small molecule that, according to Pelage, acts on the metabolic switch that keeps hair follicle stem cells dormant, and Pelage describes it as acting on follicle stem cell metabolism. It belongs in this article because it is the only new topical with a randomized human result, and because the result is instructive. The press release describes a 4-week treatment with follow-up to 12 weeks, a responder analysis (share of participants crossing a 20 percent density threshold) rather than a mean hair count, and a subgroup (men with a higher degree of loss) for the headline number. Those are normal features of an early-phase readout and normal reasons to wait for Phase 3: responder thresholds can flatter small trials, 8 weeks is short for hair, and the full data have not been published in a journal. Evidence tier: human RCT, early phase, company-reported.

How the tiers compare

Line the evidence up and the picture is simple. Minoxidil and finasteride: human RCTs, hundreds to thousands of participants, 48 weeks to 2 years, objective counts, regulatory approval. PP405: one company-reported early-phase RCT of 78 people with a short window, Phase 3 pending. GHK-Cu: rodent follicle enlargement from 1993 and a cosmetic literature. AHK-Cu: follicles in a dish, once, in 2007. PTD-DBM: mice, once, in 2017. What the peptides share is a plausible mechanism (copper delivery and angiogenesis for the copper peptides, Wnt activation for PTD-DBM) and an absence of the study that would test it in people. Plausible mechanisms are cheap in hair biology; most of the molecules that grow hair in mice never grow it in men.

The bottom line

As of September 2026, no peptide has a controlled human hair-growth trial. Anyone choosing between a copper peptide serum and the approved treatments is choosing between a mechanism and a measurement. The one genuinely new human result in this space, PP405, is not a peptide, is not available, and is one Phase 3 away from meaning anything.