Do hair growth serums work?

Last updated: October 2026

Some ingredients have evidence, but it is uneven. Topical minoxidil, one of only two FDA-approved medicines for pattern hair loss, needs at least 4 months of use, and most new hair is lost within months of stopping. Cosmetic scalp serums with caffeine, peptides or rosemary oil rest on small trials, often industry-linked. In the US, any product promising to regrow hair is regulated as a drug.

What makes a hair growth serum a drug rather than a cosmetic?

In the United States, intended use decides whether a product is a cosmetic or a drug, and label and advertising claims help establish it². FDA names claims that a product will restore hair growth as an example of claims that make a product a drug, even when it is marketed as a cosmetic².

A 1989 federal rule goes further for over-the-counter products. It lists ingredients that have been marketed as hair growers or for hair loss prevention, including amino acids, biotin and all other B vitamins, dexpanthenol, nucleic acids and wheat germ oil, and states that there is a lack of adequate data to establish general recognition of the safety and effectiveness of these or any other ingredients for that use¹. Any over-the-counter product labeled or promoted as a hair grower or for hair loss prevention is regarded as a new drug that needs an approved new drug application¹.

Canada draws a similar line. Under the Food and Drugs Act, a cosmetic is used for cleaning, improving or altering the complexion, skin, hair or teeth, while a drug is used to diagnose, treat, mitigate or prevent a disease, disorder or abnormal physical state⁸.

Which hair loss treatments have the strongest evidence?

The only FDA-approved medications for androgenetic alopecia, the common pattern form of hair loss, are finasteride and minoxidil⁶. Topical minoxidil is used to stimulate hair growth and to slow balding, works best in people under 40 whose hair loss is recent, and has no effect on a receding hairline³. Men may also take finasteride or dutasteride, and a hair transplant is another option a clinician may recommend⁴.

Popular cosmetic actives sit on a thinner base: a 2025 review found most were tested in combination formulas, with small samples and conflicts of interest⁵.

Do scalp serums for thinning hair work?

Some cosmetic actives have encouraging early data. Caffeine is thought to counter the follicle shrinkage driven by dihydrotestosterone (DHT) by inhibiting phosphodiesterase, and in a double-blinded trial in 40 Korean men and women, a daily 0.5% caffeine shampoo produced significant differences in hair density compared with a vehicle shampoo after 8, 16 and 24 weeks⁵.

Rosemary oil (Rosmarinus officinalis) has drawn the most attention lately⁶. In a single-blind randomized trial, 100 men aged 18 to 49 with androgenetic alopecia used rosemary oil or 2% minoxidil for 6 months; both groups had a significant increase in hair count with no significant difference between them, and scalp itching was more frequent with minoxidil⁶.

The review authors call for well-designed comparative studies and see these agents mainly as add-ons or for people who do not tolerate standard therapies⁵.

Do peptide serums help with hair growth?

Peptide hair serums most often use acetyl tetrapeptide-3, a biomimetic peptide, paired with red clover extract rich in biochanin A⁵. Biochanin A inhibits 5-alpha reductase, the enzyme that makes DHT, in laboratory work⁵.

The human data are small. In 30 men with androgenetic alopecia, a lotion with the complex used daily for 4 months raised the ratio of growing (anagen) to resting (telogen) hairs by 46%, compared with a 33% fall on placebo⁵. In a 24-week, triple-blinded randomized trial in 32 men and women, an extract with biochanin A, acetyl tetrapeptide-3 and ginseng performed comparably to 3% minoxidil with no local adverse reactions⁵.

Almost all of these formulas also contain vitamins, minerals or other additives, so it is hard to tell which ingredient is responsible, and some studies were company-sponsored⁵.

Why is your hair thinning, and when should you see a doctor?

Some shedding is normal. The scalp holds about 100,000 hairs, and losing roughly 50 to 200 a day is typical⁴. About 80% of men show signs of male pattern baldness in their lifetime⁴.

In pattern hair loss, DHT binds to androgen receptors in the scalp and shrinks the follicle; biopsies show a ratio of growing to resting hairs near 5 to 1, against about 12 to 1 in people without it⁶. Sudden heavy shedding is often different: physical or emotional stress, a high fever, childbirth, major surgery or a crash diet low in protein can cause shedding weeks to months later, which usually decreases over 6 to 8 months⁴. Some medicines, anemia and thyroid disease can also cause it⁴.

• See a clinician if hair loss follows an unusual pattern, or comes on fast or at an early age, such as in your teens or twenties⁴.
• See a clinician if there is pain or itching, red or scaly scalp skin, bald spots in the beard or eyebrows, or signs of a scalp infection⁴.

How do you choose and use a scalp serum?

Start with the claim on the label. A serum that promises to restore hair growth is making a drug claim under US law². Minoxidil goes on a dry scalp, never on sunburned or irritated skin³.

Give any product time: the cosmetic trials above ran 4 to 6 months^5,6. Scalp itching, dryness, scaling, flaking and burning are the common reactions to minoxidil³, so introduce one new scalp product at a time and patch test first if your skin reacts easily.