Does TRT cause hair loss?

The mechanism: testosterone → DHT → follicle miniaturization

Male androgenetic alopecia is an androgen-driven process. As the Endotext chapter on Male Androgenetic Alopecia (Asfour, Cranwell, Sinclair, 2023) describes it, the enzyme 5-alpha-reductase converts testosterone to the more active metabolite DHT; “DHT binds the androgen receptor with 5 times the avidity of testosterone,” and DHT binding to the scalp hair follicle androgen receptors produces male androgenetic alopecia. The histological hallmark is progressive hair-follicle miniaturization — shorter growth phases and smaller hairs.

Genetic susceptibility decides who is affected

Whether this process happens is largely inherited. The same source reports that “twin studies identified heredity as accounting for around 80% of the predisposition to baldness,” following a polygenic pattern rather than simple dominance. The androgen-receptor gene is described as necessary but not sufficient — androgens drive the process, but only in men whose genetics make their follicles susceptible.

Where TRT fits — and what is not established

Testosterone therapy raises circulating androgens, including the substrate 5-alpha-reductase converts to DHT — so mechanistically it can accelerate hair loss in men already genetically susceptible to androgenetic alopecia. But the cited literature stops there: the androgenetic-alopecia source does not address exogenous testosterone therapy and scalp hair loss, and provides no TRT-specific incidence. What is established is the DHT mechanism and its genetic gating; what is not established, in these sources, is how often — or how much — hair loss occurs specifically as a result of testosterone therapy. The historical observation that castrated men did not develop pattern baldness unless given testosterone shows androgen dependence, not a therapy-specific rate.

The honest bottom line

So the answer is neither “yes, TRT causes hair loss” nor “no, it doesn't.” Hair loss on testosterone therapy depends on individual genetic susceptibility to androgenetic alopecia through the DHT pathway; the mechanism is well-documented, but the cited literature does not quantify a TRT-specific outcome. Testosterone therapy is a prescription treatment, and questions about a specific person's risk are clinical ones for a licensed physician. This page describes what the sources establish and where they are silent — it is not medical advice.

• DHT (from testosterone via 5-alpha-reductase) drives androgenetic alopecia; DHT binds follicle receptors ~5× more avidly than testosterone (Endotext, Asfour 2023).
• Heredity accounts for ~80% of the predisposition — genetics gate who is susceptible.
• TRT raises androgens, but the cited literature establishes no TRT-specific hair-loss rate — mechanism known, outcome not quantified.