Testosterone Therapy (TRT) and Hair Loss: What Happens to DHT, and What the Evidence Actually Shows

Who This Is For#

This guide is for you if:

• You are on testosterone replacement and have noticed thinning at the temples or crown
• You are considering TRT and want to know what it does to DHT
• You have read that gel raises DHT more than injections do and want the actual data
• You want to know whether a 5-alpha-reductase inhibitor is used alongside testosterone
• You take testosterone as gender-affirming therapy and want the hair data

This guide is NOT for you if:

• You want the mechanism in depth; read DHT and Hair Loss
• You want treatment options for pattern loss; see Androgenetic Alopecia
• Your loss is patchy, painful or sudden; see When to See a Dermatologist
• You are asking about a supplement, not a prescribed hormone; see Creatine and Hair Loss

What Testosterone Therapy Does to DHT#

Testosterone is the precursor; DHT is the metabolite that acts on hair#

The AndroGel label is explicit: "The major active metabolites of testosterone are estradiol and dihydrotestosterone (DHT)" [1]. The cypionate label puts it in receptor terms — "In many tissues the activity of testosterone appears to depend on reduction to dihydrotestosterone, which binds to cytosol receptor proteins" [2] — and a review of androgen replacement calls testosterone, "For some androgen-dependent functions", "a pro-hormone, peripherally converted to 5alpha-dihydrotestosterone (DHT) and 17beta-estradiol (E2)" [5].

So raising testosterone raises DHT. That is not a flaw in the drug; AndroGel describes the rise as indicating "enhanced availability of the major physiologically active androgen" [1].

The route matters, and the formulations were compared with each other only for hormones#

Formulations move DHT differently. AndroGel reports the mean steady-state DHT/T ratio as "0.23 to 0.29 (50 mg of AndroGel 1%/day)" and "0.27 to 0.33 (100 mg of AndroGel 1%/day)," adding that the ratio "stayed within the normal range" [1].

A head-to-head study compared a buccal system, "30 mg twice daily," with "AndroGel 5 g containing 1% (50 mg) T" daily over "14 days" [6]. Mean DHT on day 14 was "1.9 +/- 1.4 nmol/L (0.55 +/- 0.42 ng/mL)" on the buccal system against "3.2 +/- 1.3 nmol/L" on the gel, "significant (p = 0.012)"; the paper puts the "upper level of normal" at "2.9 nmol/L; 0.85 ng/mL" [6]. The T/DHT ratio separated them further: "9.3" versus "5.0," on a stated normal of "9-12" [6].

The androgen-replacement review adds more route effects: "Scrotal testosterone patches generate supraphysiological plasma DHT levels, which is not the case with the nonscrotal testosterone patches" [5]; one regimen at "80 mg twice daily" kept testosterone "largely in the normal range, but plasma DHT tends to be elevated" [5]; and parenteral testosterone undecanoate gave "normal plasma levels of testosterone for 12 weeks, with normal plasma levels of DHT and E2 also" [5].

None of these formulation comparisons followed scalp hair. The step from a higher DHT/T ratio to a visible hairline change is an inference none of them made directly.

What the Drug Labels Say About Hair#

One quantified rate, from a trial too short to detect pattern loss#

The only quantified alopecia figure in either label comes from AndroGel's 180-day controlled trial in hypogonadal men: "Alopecia — 1% / 0% / 1%" across the 50 mg, 75 mg and 100 mg dose groups, alongside "Acne — 1% / 3% / 8%" [1]. Alopecia appears again in the postmarketing list, without a rate [1].

Take that figure as a fact about the trial, not a risk estimate. The dose groups were small and pattern loss is slow — a review of testosterone therapy in trans men notes that "facial hair and alopecia continue to develop after 1 year" [13]. The acne gradient in the same table rises with dose, so the trial could detect a fast androgenic skin effect; the flat alopecia line mainly shows hair had not had time to move. Other short studies say the same by omission: a three-month gel trial reported "No drug-related AEs occurred in the TTG group" [8], and a review of another gel lists application-site reactions, not hair [7].

The cypionate label names baldness but gives no rate#

The testosterone cypionate label lists, among reactions that "have occurred with some androgens," this line under skin and appendages: "Hirsutism, male pattern of baldness, seborrhea, and acne" [2]. For women it separately lists "hirsutism, virilization, deepening of voice, clitoral enlargement, breast atrophy, male-pattern baldness, and menstrual irregularities" [2]. Neither listing carries a frequency.

That is the whole quantified label evidence. A confident percentage for hair loss on TRT in cisgender men goes beyond it.

Why Susceptibility Matters More Than Dose#

DHT only acts where the follicle is genetically sensitive#

Androgenetic alopecia is defined by where the hormone lands, not by how much circulates. It is "a hair loss disorder mediated by dihydrotestosterone, the potent form of testosterone" [4], and "Hair thinning results from the effects of the testosterone metabolite dehydrotestosterone (DHT) on androgen-sensitive hair follicles" [3]. Follicles elsewhere answer the same hormone by growing more hair — which is why the cypionate label lists hirsutism and male pattern baldness in one sentence [2].

The pattern is the tell: "bitemporal recession of the frontal hairline, followed by diffuse thinning at the vertex" [3]. If that runs in your family, testosterone therapy supplies more of a signal your follicles already answer to; if it does not, it may do nothing visible to your scalp. No study quantifies what share of men starting TRT carry that susceptibility, so no honest number exists for how many will lose hair. Check your pattern against the Norwood Scale and the early signs guide.

Blood levels did not predict who lost hair#

A prospective and cross-sectional study of trans men concluded that "Dermatological outcome was not demonstrably related to individual serum T or dihydrotestosterone levels" [14]. That does not prove dose is irrelevant — it means the evidence cannot show a dose-response for scalp hair.

Anabolic Steroid Doses as the Extreme Case#

Abuse-level doses point the same direction, but no one has counted#

The cypionate label separates therapy from abuse: testosterone "has been subject to abuse, typically at doses higher than recommended for the approved indication and in combination with other anabolic androgenic steroids" [2].

For hair, the closest evidence is a dermatology review of female athletes: "hormonal alterations secondary to PES use can induce or accelerate female pattern hair loss (FPHL)," and "timely diagnosis and treatment of FPHL, alongside AAS cessation, are crucial to preventing further hair loss" [18]. The same review notes that research "has disproportionately focused on male pattern hair loss (MPHL) and male athletes utilizing PES" [18]; what is missing is a systematic review putting an incidence figure on alopecia in male anabolic-steroid users.

Finasteride Alongside TRT: What Is Known and What Is Not#

The mechanism is settled; the co-use trial data is not#

Finasteride and dutasteride "inhibit the enzyme 5α-reductase, reducing the conversion of testosterone into dihydrotestosterone, a hormone implicated in prostate enlargement and hair loss" [10]. In meta-analysis, "1 mg finasteride in men" was among treatments "superior to placebo (P < .00001)" [4].

What is missing is the trial you would want. No randomized trial has tested finasteride alongside testosterone to treat or prevent hair loss in men on TRT. The one trial combining them randomised "Sixty men aged ≥60 years" in a "2×2 factorial design" — "testosterone-enanthate (125 mg/week)", described in the trial as "a supraphysiological dose of testosterone", versus vehicle, "paired with finasteride (5 mg/day) versus placebo" — for "1 year", with cognitive, not dermatologic, endpoints [11].

A pharmacokinetic review states "No drug interactions with finasteride have been reported" [9] — an older survey of the pharmacology literature, not a safety verdict on this pairing. Whether a 5-alpha-reductase inhibitor belongs in your regimen is a decision for the prescriber managing your testosterone. The finasteride guide covers the drug alone; Topical Finasteride covers a lower-exposure route, where a phase III trial found serum DHT reduced "34.5 vs. 55.6%" for topical versus oral and a hair count change of "20.2 vs. 6.7 hairs" against placebo at week 24 [12].

Women on Testosterone#

Menopausal libido therapy — hirsutism is reported, scalp loss is not quantified#

For postmenopausal hypoactive sexual desire disorder, a review of randomized data reports that "The main side effects reported in clinical trials were increased hair growth and acne" [19] — unwanted body and facial hair, not scalp density. No study quantifies scalp hair loss in this group. If you are thinning around menopause, see Menopause and Hair Loss and Female Pattern Hair Loss.

Gender-affirming masculinizing therapy — the longest-duration hair data available#

The longest-running hair data in trans men come from "a prospective intervention study in 20 hormone naive trans men and a cross-sectional study in 50 trans men with an average of 10 years on T therapy" [14]. In it, "Only one trans man acquired mild frontotemporal hair loss during the first year of T treatment, whereas 32.7% of trans men had mild frontotemporal hair loss and 31% had moderate to severe androgenetic alopecia after long-term T therapy" [14]. Body hair moved faster: the Ferriman-Gallwey score "increased progressively from a median value of 0.5 at baseline to a value of 12 after 12 months" [14].

A retrospective cohort of "37,826 patients" found an adjusted incidence rate ratio for androgenetic alopecia on masculinizing therapy of "2.50, 95% CI 1.71-3.65" versus cisgender women, but "1.30, 95% CI 0.91-1.86" versus cisgender men — an interval crossing 1 [15]. Masculinizing therapy appears to move risk toward the male baseline rather than past it. Systematic review agrees testosterone "may increase facial and body hair growth as well as induce or accelerate AGA," while noting most studies "used grading schemes or subjective measures" [16]. A narrative review adds that alopecia in trans men "follows a clinical course similar to cisgender men," and that "The role of 5-alpha-reductase inhibitors appears more relevant in TM" [17].

What to Discuss With Your Prescriber#

What the evidence supports asking, and what it cannot answer#

Nothing here is a reason to change a prescription. These are the questions the evidence supports asking.

• Formulation and DHT. The routes measured differ in what they do to DHT [5][6]. Whether that matters for your scalp is untested.
• Confirm it is pattern loss. Testosterone is not the only cause of thinning; see Hair Loss Blood Tests and Diffuse Thinning vs Pattern Baldness.
• Photographs, not impressions. Standardized photos give the prescriber something to compare against. See Tracking Hair Loss Progress.
• Treatments for the hair itself. In meta-analysis, low-level laser light therapy, minoxidil and finasteride were all "superior to placebo (P < .00001)" [4]. Which, if any, fits is the prescriber's call.
• What else is being monitored. The gel label's boxed warning concerns "Virilization... reported in children who were secondarily exposed to testosterone gel" [1] — a household risk outranking hair.

See a dermatologist without waiting if you have round, well-defined bald patches; scalp pain, burning, redness or scale; smooth shiny areas where follicle openings have disappeared; loss that arrived within days; or hair loss with fever, weight change or other systemic symptoms.

Frequently Asked Questions#

Related Resources#

• DHT and Hair Loss: the mechanism in depth
• Androgenetic Alopecia: the condition testosterone can accelerate
• Finasteride for Hair Loss: the on-treatment trial data
• Topical Finasteride: the lower-exposure route
• The Norwood Scale: identifying your pattern
• Hair Loss Blood Tests: confirming the cause
• Creatine and Hair Loss: the other DHT question
• When to See a Dermatologist: red flags