5-Alpha Reductase Explained: How Pharmaceutical and Botanical DHT Inhibition Actually Differ

18 août 2026

By Dr. Susan Lin, MD | MD HAIR | La Cañada Ventures, Inc.

You have reached the stage of research where the marketing language stops being enough. You have read that DHT is the problem. You have read that finasteride “blocks DHT” and that saw palmetto “blocks DHT,” and somewhere in the back of your mind a reasonable question has been forming: if they both block the same thing, why does one require a prescription and a conversation about pregnancy risk, and the other sit on a shelf next to the shampoo?

That question deserves a real answer, and almost nobody gives you one. Instead you get a false equivalence — the supplement world implying its botanical is a gentler finasteride, and the pharmaceutical world implying botanicals do nothing at all. Both framings are wrong.

I am Dr. Susan F. Lin, M.D. I trained at Boston University School of Medicine, I am board-certified in Obstetrics & Gynecology and in Anti-Aging Medicine (A4M), and I have been formulating for hair and skin since 2008 as the physician behind the MD® line at La Cañada Ventures, Inc. I spent my clinical years caring for exactly the patient population that pharmaceutical DHT inhibition excludes. So let me take you through the enzyme itself — what it is, where it lives, what happens when you shut it down systemically versus locally, and what each approach costs. This is the pharmacology conversation told honestly, including the parts that are not flattering to the drug-free side.

The Enzyme: What 5-Alpha Reductase Actually Does

5-alpha reductase (5αR) is an NADPH-dependent enzyme embedded in the membranes of cells in specific tissues. Its job is a single, irreversible chemical step: it takes testosterone and reduces the double bond in the A-ring of the steroid nucleus, producing 5α-dihydrotestosterone — DHT.

That one small structural change has outsized consequences. DHT binds the androgen receptor with substantially greater affinity than testosterone and dissociates from it far more slowly, so the receptor stays occupied and the androgenic signal inside the cell is amplified (Azzouni et al., 2012). Testosterone is the circulating currency; DHT is the local, concentrated, high-denomination version of it, minted on site in the tissues that carry the enzyme.

This is the architectural point most consumer content misses entirely: DHT is largely a tissue-level phenomenon, not a bloodstream phenomenon. Your scalp does not passively receive DHT from your serum. Your scalp, to a significant degree, manufactures its own. That single fact is what makes local intervention biologically coherent, and it is where this entire article is heading.

Two Genes, Two Enzymes, Two Neighborhoods

5-alpha reductase is not one enzyme. The two isoforms relevant to hair are encoded by separate genes on separate chromosomes, and they have different pH optima, different substrate affinities, and — critically — different tissue distributions.

Type I 5αR is expressed predominantly in sebaceous glands, non-genital skin including scalp skin, and the liver, and operates well at neutral-to-alkaline pH. Think of it as the enzyme of the skin surface and its appendages.

Type II 5αR is expressed in the prostate, seminal vesicles, genital skin, liver, and — importantly for us — in the hair follicle itself, with particular concentration in the dermal papilla and inner root sheath. It prefers acidic pH and has higher affinity for testosterone.

The foundational tissue-distribution work comes from Russell and Wilson’s characterization of the two-gene, two-enzyme system and from Thigpen and colleagues, who mapped isozyme expression across human tissues (Russell & Wilson, 1994; Thigpen et al., 1993). In the scalp specifically, Sawaya and Price measured both isoforms — alongside aromatase and androgen receptor — directly in hair follicles from women and men with androgenetic alopecia, and found both present and active, with meaningful differences between the sexes (Sawaya & Price, 1997).

The practical translation: the scalp follicle sits at the intersection of both enzymes. Local DHT can be generated through two doors, not one.

A Natural Experiment: What Life Without Type II Looks Like

A rare inherited condition — 5α-reductase Type II deficiency — gives us an unusually clear window into what this enzyme does across a lifetime. Individuals with the deficiency, described in a landmark series by Imperato-McGinley and colleagues, are genetically male but born with ambiguous or feminine-appearing external genitalia, because DHT is required for that development in utero (Imperato-McGinley et al., 1974).

Two observations from that population shaped modern hair pharmacology: they do not develop male pattern baldness, and they do not develop benign prostatic hyperplasia. That is the entire intellectual foundation of finasteride — if the absence of Type II activity from birth prevents pattern hair loss, perhaps inhibiting Type II in adulthood will slow it.

It is also the entire foundation of the pregnancy warning. Both conclusions come from the same observation; you cannot take the hair benefit from that natural experiment and leave the fetal development risk behind.

Pharmaceutical Inhibition: Potency at a Systemic Price

Finasteride: Type II Selective

Finasteride is a 4-azasteroid — a molecule deliberately built to resemble testosterone closely enough that the enzyme accepts it into the active site. It is selective for Type II 5αR, and at a standard 1 mg oral dose it substantially suppresses serum DHT while leaving serum testosterone essentially intact.

In the pivotal one-year trials in men with androgenetic alopecia, finasteride produced statistically significant increases in hair count and improvements in investigator-assessed appearance versus placebo (Kaufman et al., 1998). I have no interest in minimizing that. It is real, replicated, and in men clinically meaningful.

Dutasteride: Dual Inhibition

Dutasteride inhibits both isoforms, with higher potency and a far longer half-life — weeks rather than hours — producing deeper systemic DHT suppression. In a randomized comparison, dutasteride outperformed finasteride on hair count and width measures in men with male pattern hair loss (Olsen et al., 2006).

If you want the honest headline of this article, here it is: dual, systemic enzyme inhibition is the most potent DHT-suppressing strategy available, and nothing botanical approaches it. Any brand telling you otherwise is selling, not explaining.

What Systemic Suppression Costs

The reason we do not simply hand dutasteride to everyone is that the enzyme being shut off is not scalp-specific. It is expressed in the prostate, genital skin, liver, and central nervous system, and systemic inhibition suppresses DHT everywhere the enzyme lives.

A systematic review of the 5αR inhibitor literature documents the recognized profile: sexual adverse effects including decreased libido, erectile dysfunction, and ejaculatory disorders; gynecomastia; and mood changes, with ongoing scientific debate about symptom persistence in a subset of users after discontinuation (Hirshburg et al., 2016). Absolute rates in controlled trials are low and placebo effects in this domain are substantial — but “low” is not “zero,” and a patient is entitled to weigh a low-probability, high-salience risk however he or she chooses.

Teratogenicity: The Non-Negotiable Line

For women, the decisive issue is not libido. It is fetal development. DHT is required for normal differentiation of male external genitalia during the first trimester, and a 5αR inhibitor crossing the placenta in a woman carrying a male fetus can interfere with that process. This is why finasteride and dutasteride carry explicit contraindications in women who are or may become pregnant, and why the labeling instructs that females who are pregnant or may become pregnant should not even handle crushed or broken tablets — absorption through skin is a real, if small, route (Hirshburg et al., 2016; finasteride prescribing information).

Layer in dutasteride’s multi-week half-life, which extends the window of concern long past the last dose, and the picture for a woman in her 30s or 40s who is pregnant, nursing, trying to conceive, or simply not ruling it out becomes clear. Systemic 5αR inhibition is not a realistic daily companion. That is not a marketing observation — it is the clinical reality that defined my patient population for years, and the reason MD HAIR exists in the form it does.

Competitive, Non-Competitive, and Mechanism-Based Inhibition — In Plain Language

To compare pharmaceutical and botanical inhibition fairly, you need one piece of enzymology. Picture the enzyme as a lock and testosterone as its key.

Competitive inhibition is a decoy key. The inhibitor is shaped enough like the substrate to slide into the same keyhole, and while it sits there, testosterone cannot get in. The defining feature is that it is a numbers game: flood the system with enough testosterone and it out-competes the decoy. Dose-dependent, and in principle reversible.

Non-competitive inhibition is a different attack. The inhibitor binds somewhere other than the keyhole and changes the enzyme’s shape so the lock no longer turns properly. Because it is not fighting for the same seat, adding more testosterone does not rescue the reaction.

Mechanism-based (irreversible) inhibition is the pharmaceutical trick. Finasteride enters the active site as a substrate mimic and the enzyme begins to process it — but the reaction produces an intermediate that binds essentially permanently to the enzyme-cofactor complex, taking that enzyme molecule out of service for good. The cell must synthesize new enzyme to recover. This is why a once-daily 1 mg dose produces suppression far out of proportion to the drug’s short plasma half-life (Bull et al., 1996).

Botanical 5αR-interacting compounds, as characterized in laboratory enzyme systems, generally behave as reversible inhibitors — competitive, non-competitive, or mixed depending on the compound and the assay. Plant sterols such as beta-sitosterol and the fatty acid fractions of saw palmetto have been examined in exactly these terms in vitro, and a small randomized trial of botanically derived 5αR inhibitors reported improvement in androgenetic alopecia (Prager et al., 2002).

Hold the two pictures side by side, because this is the whole comparison in one frame. The pharmaceutical permanently disables enzyme molecules throughout the body at a dose small enough to swallow once a day. The botanical reversibly occupies or perturbs enzyme activity wherever it is physically present, for as long as it is present, and then washes out. Reversibility is a weakness if your goal is maximum systemic suppression; it is a feature if your goal is a locally acting intervention with a shallow, self-limiting footprint — precisely the goal for a woman of reproductive age.

Botanical Inhibition: Trading Potency for a Different Risk Ledger

Here is what changes when the intervention is applied to the scalp rather than swallowed.

The exposure is regional, not systemic. A topically applied botanical acts where it is placed and where it penetrates. Serum DHT is not meaningfully suppressed — so the prostate, the CNS, and, critically, a developing fetus are not targets of the intervention. The pharmacology is also reversible and self-limiting: no permanently inactivated enzyme pool, no weeks-long washout, no residual suppression after you stop.

The evidence base is different in kind, and I will not blur that. Botanical 5αR research consists largely of enzyme-level and cell-model work — in vitro and ex vivo studies — plus a small number of modest human trials. I also want to be precise about where our own lead botanical sits in that picture, because it is not in the enzyme column at all. I cannot tell you that lilac-derived verbascoside inhibits 5-alpha reductase; the peer-reviewed work on this molecule does not test that. What it does show is something one step further down the same pathway, and in my view more interesting. In controlled laboratory studies on human dermal papilla cells — the cells at the base of the follicle — verbascoside induced cell proliferation, prevented testosterone-induced cell death, and reduced the release of pro-inflammatory signals including IL-1α, IL-6, IL-1β and TNF-α (Wisuitiprot et al., 2022). These are cell studies, not human trials, and the authors state that clinical study is still needed. So the androgen story for this ingredient is about the cell that dies, not the enzyme that fires. And nothing here is a drug: MD® products are cosmetics and dietary supplements, not FDA approved, and not intended to diagnose, treat, cure, or prevent any disease, including androgenetic alopecia.

So the honest ledger reads: pharmaceutical inhibition buys potency and a randomized-trial evidence base, and charges systemic androgen suppression, a documented adverse-effect profile, teratogenic risk, and indefinite dependence on continued dosing. Botanical approaches buy a locally confined, reversible, drug-free intervention — with your own physician’s sign-off — and charge potency and evidentiary depth. Neither column is empty, and anyone who shows you only one column is not educating you.

The Bottom Line

5-alpha reductase converts testosterone into DHT in two isoforms with different tissue addresses — Type I in sebaceous glands and scalp skin, Type II in the follicle’s dermal papilla, prostate, and genital tissue — and both are measurable in the human scalp follicle (Sawaya & Price, 1997). Finasteride inhibits Type II through mechanism-based, essentially irreversible inactivation; dutasteride inhibits both isoforms with greater potency and a much longer half-life. Both are more potent than any botanical, and both carry a systemic adverse-effect profile plus a teratogenic risk that takes them off the table for women who are pregnant, nursing, or may conceive.

Botanical compounds studied against the same enzyme system act reversibly and, applied topically, regionally — trading potency for a footprint appropriate to that excluded population. That trade is not a marketing compromise; it is a clinically reasoned choice about which risks a person should be asked to carry in exchange for what benefit. Understand the trade, then make it on purpose, with your own physician, rather than by default.

Dr. Susan Lin’s Clinical Perspective

“Let me say the unpopular thing plainly: systemic 5-alpha reductase inhibition is more potent than anything I formulate, and any brand that pretends otherwise has forfeited its credibility. What I dispute is not finasteride’s potency — it is the assumption that potency is the only axis that matters. As an obstetrician-gynecologist, I spent years with women for whom a teratogenic systemic drug was simply unavailable: pregnant, nursing, trying to conceive, or unwilling to accept systemic androgen suppression for a cosmetic endpoint. For that population the question is not ‘what is strongest,’ but ‘what is best available inside my actual constraints.’ A locally acting, reversible, drug-free approach grounded in the same enzyme biology is a rational answer — provided it is described in the language of mechanism and never dressed up as a clinical cure.”

— Dr. Susan F. Lin, M.D., Physician Formulator, MD HAIR

Mechanism Spotlight: Why Local Enzyme Activity Makes Local Intervention Coherent

The most common objection to topical DHT strategies is intuitive but mistaken: if DHT is a hormone in your blood, how could anything you rub on your head matter? The answer is that scalp DHT is substantially made on site. 5-alpha reductase is a membrane-bound enzyme expressed in the cells of the pilosebaceous unit itself — Type I concentrated in the sebaceous gland and surrounding skin, Type II in the follicle’s dermal papilla and inner root sheath (Russell & Wilson, 1994; Thigpen et al., 1993; Sawaya & Price, 1997). Testosterone arrives from circulation, but its conversion to the higher-affinity androgen happens locally, and the DHT produced acts on androgen receptors in the immediate neighborhood before it is cleared. That is why serum DHT correlates so imperfectly with scalp involvement, and why Sawaya and Price measured isoform balance in follicular tissue rather than in blood. If the relevant enzymatic step occurs within millimeters of the follicle, an intervention delivered to those millimeters is engaging the pathway where it actually runs. The constraint stops being conceptual and becomes purely a formulation problem — getting the molecule through the stratum corneum, into the follicular reservoir, and holding it there long enough to matter.

MD HAIR Product Recommendation

MD Nutri Hair™ — Hair Density Supplement

If this article convinces you of one thing, I hope it is that the DHT pathway is worth engaging thoughtfully rather than aggressively. MD Nutri Hair™ is the internal half of that approach: lilac stem-cell extract standardized for verbascoside, alongside flaxseed and lignan powders, biotin, vitamin E, and niacinamide, nourishing the hair’s natural cycle from within, where topicals cannot reach. Because the verbascoside is standardized, the molecule described above — the one that, in laboratory studies on human dermal papilla cells, prevented testosterone-induced cell death and reduced the release of pro-inflammatory signals including IL-1α, IL-6, IL-1β and TNF-α — is present at a known, reproducible level in every lot. That published work used verbascoside sourced from Acanthus, not lilac: the same molecule from a different plant, and not a study of our own material.

One easy capsule a day, drug-free and hormone-free, physician-formulated by Dr. Susan F. Lin, M.D. and manufactured in FDA-registered, GMP-compliant facilities in the USA. In a 30-day in-office consumer use study of MD Nutri Hair™ (30 subjects, outcomes self-reported), 95% saw improved hair appearance, 90% reported better manageability, and 75% reported increased fullness. Individual results vary; studies on file. MD Nutri Hair™ is a dietary supplement, not a drug, and is not intended to diagnose, treat, cure, or prevent any disease. Because there are no clinical data in pregnant or breastfeeding women, we do not advocate using MD HAIR products during pregnancy or lactation.

Genuine MD HAIR and MD Nutri Hair™ products are sold only through mdhair.com, md-factor.com, and the official La Cañada Ventures, Inc. stores on Amazon and Walmart. If you purchased elsewhere, we cannot verify authenticity, storage conditions, or lot integrity.

References

Russell DW, Wilson JD. (1994). Steroid 5α-reductase: two genes/two enzymes. Annual Review of Biochemistry, 63, 25–61. PubMed
Thigpen AE, Silver RI, Guileyardo JM, Casey ML, McConnell JD, Russell DW. (1993). Tissue distribution and ontogeny of steroid 5α-reductase isozyme expression. Journal of Clinical Investigation, 92(2), 903–910. PubMed
Azzouni F, Godoy A, Li Y, Mohler J. (2012). The 5 alpha-reductase isozyme family: a review of basic biology and their role in human diseases. Advances in Urology, Article ID 530121. PubMed
Sawaya ME, Price VH. (1997). Different levels of 5α-reductase type I and II, aromatase, and androgen receptor in hair follicles of women and men with androgenetic alopecia. Journal of Investigative Dermatology, 109(3), 296–300. PubMed
Imperato-McGinley J, Guerrero L, Gautier T, Peterson RE. (1974). Steroid 5α-reductase deficiency in man: an inherited form of male pseudohermaphroditism. Science, 186(4170), 1213–1215. PubMed
Kaufman KD, Olsen EA, Whiting D, et al. (1998). Finasteride in the treatment of men with androgenetic alopecia. Journal of the American Academy of Dermatology, 39(4), 578–589. PubMed
Olsen EA, Hordinsky M, Whiting D, et al. (2006). The importance of dual 5α-reductase inhibition in the treatment of male pattern hair loss: results of a randomized placebo-controlled study of dutasteride versus finasteride. Journal of the American Academy of Dermatology, 55(6), 1014–1023. PubMed
Hirshburg JM, Kelsey PA, Therrien CA, Gavino AC, Reichenberg JS. (2016). Adverse effects and safety of 5-alpha reductase inhibitors (finasteride, dutasteride): a systematic review. Journal of Clinical and Aesthetic Dermatology, 9(7), 56–62. PubMed
Bull HG, Garcia-Calvo M, Andersson S, et al. (1996). Mechanism-based inhibition of human steroid 5α-reductase by finasteride: enzyme-catalyzed formation of NADP–dihydrofinasteride, a potent bisubstrate analog inhibitor. Journal of the American Chemical Society, 118(10), 2359–2365. DOI
Prager N, Bickett K, French N, Marcovici G. (2002). A randomized, double-blind, placebo-controlled trial to determine the effectiveness of botanically derived inhibitors of 5-alpha-reductase in the treatment of androgenetic alopecia. Journal of Alternative and Complementary Medicine, 8(2), 143–152. PubMed
Wisuitiprot V, et al. (2022). Effects of Acanthus ebracteatus Vahl. extract and verbascoside on human dermal papilla and murine macrophage. Scientific Reports, 12, 1491. PubMed
Finasteride tablets — FDA prescribing information (pregnancy contraindication; handling of crushed or broken tablets). DailyMed

Dr. Susan F. Lin, M.D. is the physician formulator behind MD HAIR and MD Nutri Hair™, product lines of La Cañada Ventures, Inc. — physician-formulated since 2008 under the MD® mark. She trained at Boston University School of Medicine, is board-certified in Obstetrics & Gynecology and in Anti-Aging Medicine (A4M), and is the named inventor on U.S. Patent No. 8,206,695 (the MD® lash formulation).

MD HAIR topical products are cosmetics manufactured in FDA-registered, GMP-compliant facilities; facility registration is not product approval by the FDA. MD Nutri Hair™ is a dietary supplement. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Individual results vary. This article is for educational purposes and does not constitute medical advice. Do not start, stop, or change any prescription medication — including finasteride or dutasteride — without consulting your own physician. Because there are no clinical data in pregnant or breastfeeding women, we do not advocate using MD HAIR products during pregnancy or lactation.