GHK-Cu peptide and hair density: what trichologists get right and wrong

What did @thehealthyhur actually say?

The creator, presenting as a certified trichologist, reviewed The Ordinary Multi-Peptide Serum for Hair Density and gave it a cautious thumbs up, mostly on price and texture. She singled out caffeine as her favorite ingredient, called out acetyl tetrapeptide-3 as something "compared to Rogaine when mixed with a few other natural ingredients," and was honest that the remaining ingredients didn't impress her. Her bottom line: this is a support product for people who aren't experiencing serious hair loss, not a treatment for clinical conditions like androgenetic alopecia. That's a more responsible framing than most hair-product TikToks manage, and it deserves credit upfront.

She also name-dropped a competing caffeine scalp treatment by "the enchilists" (almost certainly The INKEY List), positioning The Ordinary version as comparable. That's a fair market comparison, even if the science behind both products is modest.

Does the science back this up?

Caffeine has genuine, if limited, research behind it for hair growth, and the peptide claim is technically defensible but overstated. The Rogaine comparison is where things get shaky.

On caffeine: Fischer et al. (2007, International Journal of Dermatology) showed caffeine inhibits DHT-related suppression of hair follicle growth in vitro. A later study by Bussoletti et al. (2011, Journal of International Medical Research) found topical caffeine improved hair density in a small clinical trial. The mechanism, blocking phosphodiesterase and reducing the effects of DHT at the follicle level, is plausible. But in vitro is not the same as a well-powered clinical trial, and the evidence base here is nowhere near what exists for minoxidil.

On acetyl tetrapeptide-3: it appears primarily in industry-funded research. One frequently cited study is by Lacount et al. (2013), but it was conducted by a supplier, not an independent lab. Comparisons to minoxidil (Rogaine) in those studies are based on in vitro cell proliferation assays, not randomized controlled trials in humans. Calling it "compared to Rogaine" is technically traceable to a source, but presenting it without that context misleads viewers into thinking the comparison has clinical weight it doesn't have.

What did they get wrong (or right)?

She got the general framing right. The Rogaine comparison needs pushback, though.

Right: Caffeine is a reasonable first ingredient to highlight. It has more independent research than most cosmetic hair ingredients. She's also correct that the serum's non-greasy texture and low price are practical selling points, and that this is not a product for people with significant hair loss. That kind of scope limitation is rare and responsible on hair-content TikTok.

Wrong, or at least incomplete: The acetyl tetrapeptide-3 and Rogaine comparison is doing a lot of work without much support. Minoxidil has decades of randomized controlled trial data and FDA approval for androgenetic alopecia. Acetyl tetrapeptide-3 does not. The creator does hedge with "when mixed with a few other natural ingredients" and "not a ton of research," but the Rogaine name-drop will stick with viewers longer than the caveat. That comparison should have been rejected outright, not softened.

• Caffeine: modest but real independent evidence
• Acetyl tetrapeptide-3: industry-funded comparisons to minoxidil, no independent RCT data
• Overall product recommendation: appropriately scoped

What should you actually know?

If you're looking at this serum because you're worried about thinning hair, the framing matters enormously. There is a significant gap between "hair support for generally healthy hair" and "treatment for hair loss."

Minoxidil, the active ingredient in Rogaine, has been studied in randomized controlled trials since the 1980s. The FDA approved it for androgenetic alopecia. Topical peptides and caffeine serums are cosmetic products in most regulatory frameworks, meaning they don't have to prove efficacy before going to market. That doesn't make them useless, but it means the burden of proof is much lower for a brand making vague "density" claims than it would be for a drug.

If you're experiencing noticeable shedding, scalp changes, or a receding hairline, a serum at this price point is not a substitute for a dermatologist or trichologist evaluation. GHK-Cu, a copper peptide that does appear in some hair serum formulations (though not prominently in this one), has some more robust research behind it, including work by Pickart and Margolina (2018, Biomolecules) on tissue remodeling, but again, in vitro and animal data dominate the literature. The creator's advice to use this as a "support product" for people without serious loss is the right call, and more TikTok creators should make that distinction explicitly.