We compared the 7 most popular hair growth serums

The Ordinary's Multi-Peptide Serum for Hair Density is the cult favorite of this category, and it earns its runner-up spot honestly. For around $29 you get a 60ml bottle — double the size of most rivals at a fraction of the price — packed with recognizable peptide technologies: REDENSYL™, Procapil™ (Biotinoyl Tripeptide-1), CAPIXYL™ (Acetyl Tetrapeptide-3), BAICAPIL™, AnaGain™ pea sprout, and caffeine, in a lightweight, water-based, vegan leave-in.

So why isn't it #1? First, the actives: for all its peptides, the formula contains no copper peptides — no GHK-Cu, no AHK-Cu — the marquee actives that define our winner, and the concentrations of each trademarked complex aren't disclosed. Second, the routine: the brand directs you to massage it into a clean, dry scalp once daily, ideally at bedtime, and lists conflicts with direct acids and vitamin C — classic no-frills DECIEM, which means more rules and less flexibility than a serum you can simply apply and style over. Reviewers also frequently mention a slightly tacky finish as it dries. And true to the brand's minimalism, there are no soothing scalp botanicals like licorice or ginseng, no published customer-results surveys, and no hand-holding.

The best pure-value formula in our review, and a worthy budget pick. But if you want copper peptides, a comfort-first formula, and a routine with fewer rules, the winner justifies the difference.

Divi is a deserved podium finisher and the only other formula in our review with a copper peptide. It's a water-based, non-greasy scalp serum with a legitimately modern ingredient list: Copper Tripeptide-1, Acetyl Tetrapeptide-3, caffeine, amino acids, and hyaluronic acid. The brand publishes results from a 12-week user study, and the daily leave-in routine mirrors what we like about our winner.

Where it falls short is depth and value. Divi is built around one copper peptide, where Rootwella pairs GHK-Cu with a complementary AHK-Cu peptide. The formula also leans on menthol, peppermint, and eucalyptus for its signature "tingle" — a sensation some people love, but one that reviewers with sensitive scalps consistently flag as irritating, and a very different philosophy from Rootwella's soothing licorice-root approach. And at $48 for a 30ml bottle — with the deeper discounts locked behind a subscription — it's noticeably more expensive per month than our winner.

A genuinely good single-peptide serum. Just narrower, tinglier, and pricier than the dual-peptide formula that won.

Vegamour's GRO Hair Serum is the polished celebrity of this category, and there's real substance behind the marketing. The vegan, plant-based formula uses phytoactives — mung bean, red clover, and curcumin stem cell extract — it's silicone-free, color-safe, and genuinely lightweight, and the brand publishes a 120-day consumer perception study behind its claims.

The problems are patience and price. Vegamour itself says most people see results within 3–4 months of daily use — the longest stated timeline in our review — and notes that if you stop, hair may gradually return to its previous state within a few months. That makes GRO a long-term commitment at a premium price: $49–$64 per 1 oz bottle, roughly a 30-day supply, with the best pricing tied to a subscription and the brand steering you toward pairing it with its supplements. It's also a botanical-only formula: no copper peptides, and none of the peptide-forward formulation that defines our top three.

A beautiful, clean serum for the committed. But you're paying the most per month for a formula with fewer modern scalp actives than the winner.

Nutrafol is the biggest name in hair wellness, and its topical serum carries that pedigree: proprietary Ashwagandha Exosomes, Irish Moss Peptides, and Pea Sprout Extract in a vegan, drug-free, fragrance-free formula that's lightweight and fast-absorbing. On texture and cleanliness of formula, it scored well with us.

The catch is what the serum is for. Nutrafol's own materials repeatedly frame it as a companion product — "for best results, pair with Nutrafol hair growth supplements," a system that runs well over $70 a month before the serum is added. Bought alone, it's a premium-priced hydrating scalp serum whose peptides are marine-derived, not the copper peptides that headline our winner, and whose headline study is notably small. As part of the full Nutrafol ecosystem it makes sense; as a standalone serum, it's an expensive supporting actor.

Mielle's Rosemary Mint Scalp & Hair Strengthening Oil is the product that made rosemary oil go viral, and at around $10 it's an easy bottle to love. It's an award-winning, versatile oil — scalp treatment, split-end sealer, hot-oil treatment — with a devoted following, especially for textured hair and protective styles.

But look at the label and you'll see why it ranks here for this job: the base is soybean and castor oil, with rosemary, peppermint, eucalyptus, and menthol on top and biotin sitting far down the ingredient list. It's a traditional heavy oil — exactly the routine that leaves fine, low-density hair looking flatter and roots looking greasier. The invigorating mint scent is strong and lingers, the menthol and camphor-rich essential oils can be a lot for sensitive scalps, and there are no peptides or modern scalp actives anywhere in the formula.

A great-value oil for conditioning and protective styles. The wrong tool for women whose main concern is a wider part and thinning-looking roots.

Botanic Hearth's Rosemary Hair Oil is the value play: a large 6.7 oz bottle of rosemary oil blended with biotin, jojoba, and castor in a carrier base of grapeseed, sunflower, and coconut-type oils, complete with a nozzle-and-comb applicator. Cruelty-free, paraben-free, and cheap per ounce — as a nourishing hair oil, it's honest about what it is.

What it isn't is a scalp serum. This is hydration and conditioning in a bottle — carrier oils plus essential oils, no peptides, no modern scalp actives, and usage instructions that in places suggest leaving it on and then washing it out with shampoo. That's the old oiling ritual: time-consuming, greasy in between, and hard to stay consistent with. For deep conditioning on thick or dry hair, it earns its price. For a daily fuller-looking-hair routine on fine hair, it's a generation behind.