Peptides and hair: what the science can actually support.

Peptides and hair... yeah. You hear a lot about it.

Between regrowth promises and shedding stories, it is hard to know what is real.

So what does the science actually say?

Peptides are already in hair products

You already see them in mainstream products from brands like The Ordinary, Typology, or Aroma-Zone.

The names that come up most often:

• Acetyl Tetrapeptide-3
• Biotinoyl Tripeptide-1
• Copper Tripeptide-1

But that is not the same topic at all as an injected peptide, the kind your influencers talk about.

The name that keeps coming up: GHK-Cu

On Reddit or TikTok, one name keeps coming back: GHK-Cu.

It is a copper peptide. People talk about it for skin, collagen, and the whole glow angle.

And for hair, many present it as a peptide that may support growth.

On social media, the feedback is often strong: more density, regrowth, baby hairs, thicker-looking hair.

But on the science side, the evidence is much more modest.

Peptides and hair shedding

Myth or reality?

Under reta or other GLP-1s, some people report heavier hair shedding.

But the cause is probably not the peptide itself.

The real issue is often:

• rapid weight loss
• calorie deficit
• metabolic stress

That can trigger temporary shedding called telogen effluvium.

What the science says today

On the shedding side: studies do confirm an increased risk on GLP-1s. A systematic review of 24 studies, and a cohort published in 2026.

And the one that produces the most weight loss is also the one most frequently linked to shedding. In the 2025 review, tirzepatide comes up most often. That is the strongest argument for weight loss being the cause, rather than the molecule.

My own case, on reta: 4.2 kg in 2 weeks, and more shedding than usual.

I stopped reta. The shedding stopped. Today there is no lasting impact on my hair.

And if it happens, it grows back

Shedding starts two to three months after the trigger.

It lasts three to six months.

Then hair grows back in the affected areas.

It is not a permanent loss. It is a delay.

So, does a peptide regrow hair?

Yes, studies do show positive effects. Just not on the peptide everyone talks about.

A penta-peptide, Gly-Pro-Ile-Gly-Ser, was tested in 22 men over four months, double-blind against placebo. The proportion of thick hair rose significantly, vellus hair fell, and blinded reviewers graded the appearance of baldness as improved on photographs.

A second randomised placebo-controlled study shows a benefit of biomimetic peptides in alopecia areata. But alopecia areata is an autoimmune condition: it is not the same subject as ordinary pattern hair loss.

GHK-Cu, on the other hand, has no human trial for hair. What exists is a 2007 study on isolated follicles in a lab. The peptide everyone talks about is the one with the least evidence.

And the only two proven at scale remain minoxidil and finasteride. Nothing new since 1997.

The simplest rule may be this: when it comes to hair, the promises usually move faster than the evidence.

And when a peptide starts to look like it does everything, that is usually the moment to slow down.

Until the next edition, take care.