Every follicle on your scalp runs its own clock. Over a lifetime, a single follicle cycles through growth, regression, and rest somewhere between ten and thirty times, independently of the follicles around it ^[1]. That independence is why a healthy scalp of roughly 100,000 hairs keeps a fairly steady density even though hairs are always falling out ^[1].

How do hair growth ingredients work? The ones with real evidence behind them act on that cycle. Some keep follicles in their growth phase longer or help resting follicles restart. Others reduce what pushes follicles out of growth too early, such as DHT, inflammation, or a nutrient deficiency. An ingredient that can't influence the cycle can make hair look or feel better, but it can't make more of it grow.

That distinction explains most of the confusion around hair growth products. Labels tend to list ingredients without saying which part of the follicle they're supposed to reach or how strong the evidence is. So before looking at minoxidil, saw palmetto, and peptides one at a time, it helps to understand the machinery they're all trying to influence.

What Is the Hair Growth Cycle?

Researchers describe four phases: anagen (growth), catagen (regression), telogen (rest), and exogen (shedding) ^[1]. The durations differ enormously, and those differences drive almost everything about how hair loss and hair treatments behave.

Source: Natarelli et al., 2023 [1].

The length of your anagen phase sets the maximum length your hair can reach. Scalp follicles stay in anagen for two to eight years, while eyebrow follicles last only two to three months ^[1], which is why eyebrows stop at a short, fixed length and scalp hair doesn't.

Anagen also gets shorter with age, and the proportion of follicles in anagen declines ^[1]. Hair that grows for less time before resting has less time to thicken, so it tends to come in finer.

How Does Hair Growth Work Inside the Follicle?

At the base of each follicle sits the dermal papilla, a small cluster of specialized cells that controls how many matrix cells the follicle has and therefore how large the hair can be ^[1]. The matrix cells divide quickly during anagen and build the hair shaft. The dermal papilla, in other words, is the part most treatments are ultimately trying to talk to.

In a healthy scalp, growing follicles outnumber resting ones by about 12 or 14 to 1 ^[1]. In androgenetic alopecia, the common pattern form of hair loss in both men and women, that ratio falls to roughly 5 to 1 ^[1].

Dihydrotestosterone is a large part of the reason. An enzyme called 5-alpha reductase type 2 converts testosterone into DHT, which binds to androgen receptors in susceptible follicles ^[1]. There it shortens anagen and lengthens telogen ^[1]. Cycle after cycle, the follicle produces a shorter, finer hair, a process dermatologists call miniaturization.

Genetics decide how sensitive a given follicle is. Research on serum DHT has produced mixed results, and one conclusion drawn from it is that inherited follicle sensitivity to DHT may matter more than the amount circulating in the blood ^[1]. That's one reason two people with similar hormone levels can have very different hair.

How Do Hair Growth Ingredients Work? Three Levers

Nearly every evidence-backed ingredient pulls on at least one of three levers. The first is extending growth: keeping follicles in anagen longer, or nudging resting follicles back into it. The second is supply, meaning blood flow, growth factors, and signaling that support the dermal papilla. The third is removing brakes, whether that brake is DHT, inflammation, or a missing nutrient.

The table below maps the three ingredients in this article, plus supplements, onto those levers. The evidence column matters as much as the mechanism column, because a plausible mechanism in a dish is not the same thing as regrowth on a human scalp.

Sources: [1] through [5].

Minoxidil: A Prodrug That Depends on Your Follicle

Minoxidil does nothing to a hair follicle until an enzyme in the follicle's outer root sheath converts it into minoxidil sulfate, its active form ^[2]. That enzyme, a sulfotransferase called SULT1A1, varies in activity from person to person. Its activity in plucked hairs has been shown to correlate with whether someone responds to topical minoxidil ^[2].

This one detail explains a frustration many people have with the drug. Two people can apply the same product faithfully for months and see very different results, and part of that difference lives in their own follicle chemistry rather than in anything they did wrong.

Once activated, minoxidil works through several routes at once. It relaxes blood vessels and increases blood flow around the follicle, and it also has anti-inflammatory effects, induces the Wnt/β-catenin signaling pathway that governs follicle growth, and shows some antiandrogen activity ^[1]. Animal studies suggest it shortens telogen and speeds the return to anagen ^[1].

The clinical evidence is the strongest of any topical ingredient. In a meta-analysis cited in a 2023 review, people using topical minoxidil were 2.28 times more likely to show hair growth than those on placebo ^[1]. In men using the 2% solution, peak regrowth arrived after about a year of use ^[1].

Patience is built into the pharmacology. It takes roughly six months of treatment to see whether someone is responding ^[2], which is why stopping at the two-month mark usually tells you nothing. Topical minoxidil is FDA-approved as an OTC drug for pattern hair loss, sold at 2% for women and 5% for men, and it isn't approved for other types of shedding such as telogen effluvium.

Saw Palmetto and the DHT Question

A 2020 systematic review in Skin Appendage Disorders gathered five randomized clinical trials and two prospective cohort studies of saw palmetto for hair loss ^[3]. That is close to the entire clinical literature on the plant for this purpose, and it's worth knowing how small it is before looking at the numbers.

Saw palmetto, the extract of Serenoa repens berries, is thought to work on the third lever. Its proposed mechanism is antiandrogenic, and reviews of herbal treatments attribute its possible benefit to inhibition of 5-alpha reductase, the enzyme that makes DHT ^{[1], [3]}.

Across the studies in the review, 60% of participants showed improvement in overall hair quality ^[3]. Total hair count improved by 27% ^[3]. Hair density increased in 83.3% of patients, and disease progression stabilized in 52% ^[3].

Those figures deserve context. They come from small studies using different products, doses, and oral or topical forms, so they can't be pooled into one reliable effect size. The reviewers themselves framed saw palmetto as a possible option that needs larger trials, not as an established treatment.

In practice, saw palmetto sits in supplement and cosmetic territory rather than drug territory, and it's generally understood to be a gentler, weaker DHT-side approach than prescription 5-alpha reductase inhibitors. For someone with early pattern thinning who wants a botanical component in a broader regimen, that trade-off can be reasonable. For advanced loss, it isn't a substitute for medical treatment.

Peptides: One Word, Several Different Ingredients

“Peptide” on a hair label can mean very different things, and the difference decides which part of the hair it can affect. Some peptides are designed to signal to cells at the follicle. Others work on the hair shaft you can already see, repairing broken bonds in the protein structure. Collagen peptides in supplements are a third category again, delivered through digestion rather than the scalp.

Copper peptides have the most direct follicle research. In a 2007 study from Seoul National University, the copper tripeptide AHK-Cu lengthened human hair follicles kept alive in the lab and stimulated the growth of dermal papilla cells at very low concentrations ^[4]. The same research group noted that copper-peptide complexes raise production of VEGF, a growth factor linked to blood vessel formation around the follicle ^[4].

Its better-known relative, GHK-Cu, has been studied mostly for skin repair. Gene-expression research suggests it influences a wide range of genes tied to tissue remodeling and inflammation ^[5], which is why it shows up in scalp formulas even though its hair-specific evidence is thinner.

What's missing is the step from the lab dish to the scalp. There are no large randomized trials showing that a topical copper peptide serum regrows hair in people with pattern hair loss, and how much peptide actually reaches the dermal papilla through intact skin is a fair open question. Our deeper look at copper peptides walks through the research in more detail.

Bond-building peptides are a different tool for a different problem. They can make damaged, brittle hair stronger and less prone to breaking, which improves how full hair looks, but they act on hair that has already grown rather than on the follicle producing it.

Where Do Supplements Fit?

Is biotin the growth ingredient its reputation suggests? The evidence says not for most people. A 2023 review in the Journal of Clinical Medicine concluded there's no indication for biotin supplementation in healthy people who aren't deficient, and noted that biotin appears to affect hair strength rather than growth ^[1].

High-dose biotin also has a practical downside. It can interfere with certain lab tests, including thyroid and troponin measurements, producing misleading results ^[1]. Anyone taking it should mention it before blood work.

Deficiencies are where nutrition clearly matters. Iron deficiency contributes to telogen effluvium, and low zinc and low vitamin D have both been associated with hair loss ^[1]. Correcting a real deficiency can help; supplementing a nutrient you already have enough of generally doesn't, and too much of some, vitamin A being the best-documented example, can itself cause hair loss ^[1].

That's the honest role for a hair supplement: filling gaps and supporting overall hair quality, ideally alongside a topical or medical treatment that addresses the actual cause.

Why Every Honest Timeline Is Measured in Months

The cycle sets the pace, and no ingredient can rush it much. A follicle pushed into telogen rests for two to three months before a new hair even starts growing ^[1], and that new hair then needs time to become long enough to change how your scalp looks.

So the most useful thing you can do with any hair growth ingredient is give it a fair trial. For minoxidil, that means around six months before judging it ^[2], applied consistently, because gaps in use let the follicle drift back toward its old pattern. Photographs taken in the same light every month or so are far more reliable than a daily look in the mirror, since gradual change is almost impossible to see day to day.

A little extra shedding in the first weeks of minoxidil isn't unusual either, as resting hairs are pushed out by new growth behind them. If shedding is heavy or lasts longer than you expected, that's a reason to check in with a dermatologist rather than to quit on your own.

How MDhair Applies This Science

Everything above points to one practical conclusion: the right ingredient depends on which lever your hair loss actually needs. That's the premise behind MDhair's science-backed personalized treatment, delivered through telehealth. It starts with a free AI hair and scalp assessment, a short quiz plus a scalp photo that looks for the likely cause of your hair loss.

The regimen is then matched to that result. For genetic or age-related thinning, that can mean OTC minoxidil (2% for women or 5% for men) alongside a DHT-blocker serum and regrowth supplements formulated with more than 20 vitamins and plant-based complexes. Unlimited dermatologist chat support is included, with adjustments made as your progress is tracked.

In the six-month, IRB-approved clinical trial my team and I ran, published in the Journal of Drugs in Dermatology ^[6], participants on this AI-personalized approach showed a 2.8x greater improvement in hair growth at 90 days than those on the leading hair loss supplement brand. Hair quality improved 3.0x over the same comparison. Under scanning electron microscopy, hair strand damage went from Grade 2, lifted cuticles with cracks, to Grade 0, an intact cuticle, after six months. Results vary between individuals, and no regimen can promise regrowth.

Drug, Cosmetic, or Supplement: Why the Label Category Matters

The mechanisms in this article sit in three regulatory categories, and it's easy to lose track of which is which. Topical minoxidil is the only ingredient here with OTC drug status, and that status covers one use: mild-to-moderate androgenetic hair loss.

Saw palmetto, peptide serums, DHT-blocker shampoos, and hair supplements are cosmetic or supplement products instead. Claims made for supplements haven't been evaluated by the FDA, and none of these products is intended to diagnose, treat, cure, or prevent disease, whatever mechanism research sits behind their ingredients.

If you're pregnant or nursing, or you're managing a medical condition, talk with your doctor before starting anything new, including supplements. Should a topical product irritate your scalp, stop using it. And because hair loss has many possible causes, this article is general education about how ingredients work, not a diagnosis of what's happening on your own scalp.

Frequently Asked Questions

Can an ingredient restart a follicle that has stopped growing hair?

It depends on how far the follicle has gone. A miniaturized follicle that still cycles can often respond to treatment, and minoxidil's effect on the telogen-to-anagen transition is part of how it works ^[1]. A follicle lost to scarring, however, can't be revived by any topical ingredient, which is one reason early assessment matters.

Why does minoxidil work for some people and not others?

Enzyme activity is a big part of the answer. Minoxidil only becomes active once SULT1A1 in the follicle converts it, and people with lower activity of that enzyme are less likely to respond ^[2]. The type of hair loss matters too, since the drug is approved for pattern hair loss specifically.

How long do hair growth ingredients take to work?

Plan for months, not weeks. Telogen alone lasts two to three months ^[1], and minoxidil typically needs about six months before response can be judged ^[2]. Supplements that correct a deficiency follow a similar timeline, because the hair they affect has to grow in first.

The Bottom Line

Hair growth ingredients work, when they work, by influencing a cycle that runs on a scale of months and years. Minoxidil has the strongest evidence and a mechanism that partly depends on your own follicle chemistry. Saw palmetto has a plausible DHT-lowering rationale and small, encouraging studies. Copper peptides are promising in the lab and unproven on the scalp, and supplements help most when they fix a real deficiency. Knowing which lever your hair loss needs is the starting point, and MDhair's free assessment is built to answer exactly that question.

How This Article Was Researched

Evidence for this piece was drawn from peer-reviewed literature located through PubMed, including a 2023 mechanistic review of the hair cycle, a systematic review of saw palmetto trials, and laboratory studies of copper peptides. Laboratory and ex vivo findings are labeled as such rather than presented as clinical results, and MDhair's own clinical trial is cited with its actual comparison.

Sources

1. Natarelli N, Gahoonia N, Sivamani RK. Integrative and mechanistic approach to the hair growth cycle and hair loss. J Clin Med. 2023;12(3):893. doi:10.3390/jcm12030893
2. Goren A, Castano JA, McCoy J, Bermudez F, Lotti T. Novel enzymatic assay predicts minoxidil response in the treatment of androgenetic alopecia. Dermatol Ther. 2014;27(3):171-173. ResearchGate
3. Evron E, Juhasz M, Babadjouni A, Mesinkovska NA. Natural hair supplement: friend or foe? Saw palmetto, a systematic review in alopecia. Skin Appendage Disord. 2020;6(6):329-337. doi:10.1159/000509905
4. Pyo HK, Yoo HG, Won CH, et al. The effect of tripeptide-copper complex on human hair growth in vitro. Arch Pharm Res. 2007;30(7):834-839. doi:10.1007/BF02978833
5. Pickart L, Margolina A. Regenerative and protective actions of the GHK-Cu peptide in the light of the new gene data. Int J Mol Sci. 2018;19(7):1987. doi:10.3390/ijms19071987
6. Bhardwaj V, Rodgers N, Harth O, Harth Y. Artificial intelligence-based personalization of treatment regimen for hair loss: a 6-month clinical trial. J Drugs Dermatol. 2025;24(3):233-238. doi:10.36849/JDD.8611

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