How much dutasteride to reduce DHT by 50%?
Executive summary
A daily dose of about 0.1 mg of oral dutasteride is associated with roughly a 50% reduction in serum DHT at steady state in clinical observations, with that effect measured at or around 24 weeks in the studies cited (0.1 mg/day → ~50% DHT suppression) [1]. Higher standard doses (0.5 mg/day) yield far greater suppression—typically >85–92% in serum—while intradermal/scalp DHT can show different, often smaller, reductions, so the target tissue and time-course matter for any practical goal [2] [3] [4].
1. What the evidence actually measures: serum vs scalp DHT and time to effect
Most clinical trials quantify serum and intraprostatic DHT; serum reductions are consistently large with dutasteride and are reported at various time points (for 0.5 mg/day median serum DHT fell by ~85–90% within 1–2 weeks and ~90+% by 1–4 months) [2] [5], whereas scalp (target tissue for hair loss) DHT reductions are lower and more variable—one set of data reported ~51% scalp DHT reduction with 0.5 mg/day while serum fell >90% [4] [6]. This distinction matters because a 50% drop “in DHT” must be qualified: serum DHT reaches suppression faster and to a greater extent than scalp DHT in many studies [2] [4].
2. The dose that corresponds to ~50% DHT suppression
Dose–response data presented by investigators indicate that DHT suppression is dose-dependent and that approximately 0.1 mg/day of dutasteride produces about a 50% reduction in circulating DHT at the 24‑week assessment point [1]. Lower doses (e.g., 0.01 mg/day) produced <10% reductions at the same time point in the same analysis, demonstrating a steep early dose–response curve [1]. Other trials testing low but varied doses (0.02 mg, 0.1 mg, 0.5 mg) show dose-related effects on hair counts and DHT measures, supporting the 0.1 mg/day inflection for roughly half-maximal serum suppression [4].
3. Practical regimens, long half-life, and off‑label patterns
Because dutasteride has a very long half‑life, clinicians sometimes use less-than-daily regimens (for example, twice-weekly dosing is commonly reported off‑label for hair loss) and still achieve clinically meaningful DHT suppression; the ISHRS notes many hair restoration physicians prescribe less-frequent dosing because of that long half-life [7]. However, the 50% figure cited from dose–response work was observed with continuous daily dosing equivalencies (i.e., 0.1 mg/day), and intermittent schedules will yield different kinetics and time to steady state [1] [7].
4. Safety, tradeoffs, and why “how much” is not only a pharmacologic question
Higher suppression correlates with greater clinical efficacy for BPH and hair endpoints but also with higher risk of adverse events; standard approved therapy for BPH is 0.5 mg/day and that dose produces >90% serum DHT suppression while being associated with known sexual and hormonal side effects that clinicians monitor [2] [8] [4]. Studies of lower doses (e.g., 0.2 mg/day) report meaningful efficacy with potentially fewer adverse events, underscoring a clinical tradeoff between the degree of DHT suppression and tolerability [9] [10].
5. Limits of the available reporting and practical takeaways
The literature consistently shows a dose-dependent suppression of circulating DHT, and the best-supported estimate for roughly 50% serum DHT reduction is about 0.1 mg/day of dutasteride measured at ~24 weeks [1]. Important caveats are that scalp DHT and intraprostatic DHT vary from serum values (0.5 mg/day can suppress scalp DHT only ~50% in some reports while serum falls >90%) and that most large trials use 0.5 mg/day [4] [5] [3]. Individual response, target tissue, regimen frequency, and safety priorities should guide dose selection; these clinical decisions require medical oversight and are influenced by off‑label practices and differing regulatory approvals for hair loss in various countries [7] [11].