PP405 has become one of the most-searched names in hair loss, and it keeps turning up on lists of "hair peptides". Both facts need correcting before anything else. PP405 is not a peptide. The one controlled trial it has finished posted its results to the registry on 22 September 2026, and those results contain no hair count at all. This page sets out what is known, dated, and where each figure comes from. For the peptide options in the same space, see our peptides for hair growth guide.
What it is
Pelage Pharmaceuticals, a Los Angeles company, describes PP405 as "a novel, non-invasive, topical small molecule designed to reactivate dormant hair follicle stem cells". That is from its 17 June 2025 press release. Neither the release nor the trial registrations give a chemical structure. Pelage's leadership page lists two UCLA professors, William Lowry and Heather Christofk (the latter as co-founder), whose laboratories produced the biology the drug is built on.
That biology is mouse work, and it is specific. In 2017 the UCLA group reported in Nature Cell Biology that hair follicle stem cells wake up when their metabolism shifts towards lactate. Blocking pyruvate's entry into mitochondria pushed dormant follicles into a new growth cycle in mice (Flores 2017). A 2021 follow-up, with an author affiliated to Pelage, reported the same effect in mouse models of hair loss caused by age, repeated chemotherapy and stress. It described "histologically normal hair follicles within 30-40 days" (Flores 2021). How PP405 relates to the tool compounds in those papers is not public.
Why it appears on peptide lists
It shares a news cycle, not a chemistry. Consumer pages group it with peptide hair products. Our hair hub has flagged the mislabel since it first covered PP405. The practical consequence matters: nothing sold as a "peptide hair serum" contains PP405, because PP405 is not sold at all.
The phase 2a trial, as registered
| Item | Registered and posted (NCT06393452) |
|---|---|
| Who | 78 adults aged 18–55 with androgenetic alopecia, men and women |
| Arms | PP405 0.05% gel (51) or vehicle gel (27), once daily to the scalp |
| Treatment | 28 days blinded, follow-up to day 84; then an open-label extension in which 20 people from the vehicle arm used PP405 for 3 months |
| Started / completed | 5 June 2024 / 1 October 2025 |
| Results first posted | 22 September 2026 |
| Primary outcomes | Adverse events, skin tolerability, vital signs, weight, ECG, laboratory values |
| Secondary outcomes | Plasma PP405 levels |
| Hair count or density | Not registered, not posted |
The trial was registered as a safety and pharmacokinetic study, and that is what it reported.
Where the 31% comes from
The efficacy figure quoted everywhere comes from the June 2025 press release. At week 8, "31% of those treated with PP405 exhibited a greater than 20% increase in hair density, compared to 0% of patients responding in the placebo group". That applies to men with a higher degree of hair loss, a subgroup of the 78. The release also claims "new hair growth from follicles where no hair was previously present".
None of that is in the registered outcomes. That does not make it false. It does mean it cannot be checked. There is no posted denominator for the subgroup, no definition of "higher degree", no method for measuring density, and no confidence interval. Until a paper or the next trial reports it, it is a company statement about a subgroup of a 78-person safety study.
What the posted results do show
Side effects. In the randomized period, 22 of 51 people on PP405 (43%) and 10 of 27 on vehicle (37%) reported at least one adverse event. The most common was itching at the application site: 7 of 51 on PP405 against 2 of 27 on vehicle. Redness at the site was 4 against 3. The only serious adverse event was an upper-arm fracture, in the vehicle group. In the open-label extension, 8 of 20 reported an event and none was serious.
Blood levels. PP405 was not detected in plasma at any sampling point. The posted mean was 0 ng/mL two hours after application on days 1, 14 and 28, and again on days 1, 28, 56 and 84 of the extension. For a topical drug meant to act in the scalp, that is the intended result. It also explains why the vital-sign and ECG changes were small and similar between arms.
What phase 3 will measure
A phase 2/3 trial (NCT07819435) was first posted on 15 September 2026 and was not yet recruiting when read. It plans 600 adult men, PP405 0.05% gel against vehicle. Its primary outcome is the change in non-vellus hair count in a target area at week 24, the standard endpoint for pattern hair loss trials. That will be the first registered efficacy result for PP405. The June 2025 release said phase 3 would study "men and women". The registration, as posted, enrols men only.
For comparison, the treatments PP405 is measured against in the press coverage are minoxidil and finasteride, both approved for pattern hair loss. How peptide options compare with them is set out in peptides for men and in our hair thickness guide, which covers what a density figure does and does not measure.
What would change this page
The phase 2a efficacy data published with a method and a denominator. The phase 2/3 trial recruiting, or reporting. A disclosed structure. Any of these would be reported here, dated.
Sources
- Pelage Pharmaceuticals, "Pelage Pharmaceuticals announces positive phase 2a results…", press release, 17 June 2025, syndicated on Yahoo Finance, read 2026-09-23.
- ClinicalTrials.gov NCT06393452: protocol, participant flow, outcome measures and adverse events, results first posted 2026-09-22, read 2026-09-23.
- ClinicalTrials.gov NCT07819435: phase 2/3 in adult males, first posted 2026-09-15, read 2026-09-23.
- Flores A, et al. (senior authors Christofk HR, Lowry WE). Lactate dehydrogenase activity drives hair follicle stem cell activation. Nat Cell Biol 2017;19(9):1017-1026. PMID 28812580.
- Flores A, Choi S, Hsu YC, Lowry WE. Inhibition of pyruvate oxidation as a versatile stimulator of the hair cycle in models of alopecia. Exp Dermatol 2021. PMID 33739490 (lists a Pelage Pharmaceuticals affiliation).
- Agrawal A, et al. Emerging pharmacotherapies for androgenetic alopecia. Expert Opin Pharmacother 2026. PMID 42290527, the one PubMed record for "PP405" on 2026-09-23.
- Pelage Pharmaceuticals, team page, pelagepharma.com/team, read 2026-09-23.