Dutasteride is a dual inhibitor of both type I and type II 5-alpha reductase — the enzymes responsible for converting testosterone into dihydrotestosterone (DHT). By inhibiting both isoforms, dutasteride achieves greater DHT suppression than finasteride, which targets only type II. This translates to superior clinical efficacy in multiple head-to-head trials for androgenetic alopecia.
The question is not whether dutasteride works — the evidence is clear that it does. The question is how to deliver it in a way that preserves that efficacy while protecting the patient from unnecessary systemic exposure.
Oral versus injectable dutasteride
Dutasteride is most commonly prescribed in an oral capsule form (0.5mg daily). While effective, systemic oral administration suppresses DHT throughout the entire body — including tissues where DHT serves important physiological functions. This whole-body suppression is the origin of dutasteride's well-documented side effect profile: reduced libido, erectile dysfunction, reduced ejaculate volume, and mood changes. A subset of patients report side effects that persist even after cessation.
I do not prescribe oral dutasteride. In my view, the systemic side effect burden of daily oral use is not justified when a more targeted delivery route is available. Instead, I use intradermal scalp injection — delivering dutasteride directly into the tissue where it needs to act.
Why injectable dutasteride
When dutasteride is injected intradermally into the scalp, it acts locally within the follicular environment — inhibiting DHT at the site of follicle miniaturisation without the same degree of systemic absorption that drives side effects via the oral route. This approach allows the therapeutic benefits of dutasteride to be realised in the scalp while substantially reducing the systemic DHT suppression that causes sexual and hormonal side effects.
Injectable dutasteride is often combined with platelet-rich plasma (PRP) in the same treatment session — pairing the anti-androgenic effect of dutasteride with the growth factor stimulation of PRP for a complementary dual mechanism.
Mechanism of action
DHT is the primary androgen responsible for follicle miniaturisation in androgenetic alopecia. It binds to androgen receptors within the dermal papilla of susceptible follicles, triggering a cascade that progressively shortens the anagen (growth) phase and reduces follicle size. By reducing intrafollicular DHT at the target site, injectable dutasteride interrupts this process — slowing or halting progression and, in many patients, contributing to measurable regrowth.
Clinical evidence
Multiple randomised controlled trials have demonstrated the superiority of dutasteride over finasteride for hair count and patient-reported outcomes in male androgenetic alopecia. Evidence for intradermal dutasteride specifically is an active and growing area of research, with studies demonstrating meaningful local DHT suppression and hair density improvements. Evidence for use in female pattern hair loss is also accumulating. Dutasteride is used off-label for hair loss — a prescribing decision made on the basis of an individual patient assessment.
Treatment details
Administration
Intradermal injection
Dutasteride is injected directly into the scalp at the treatment session. No daily oral tablet is required.
Frequency
Monthly, then 3-monthly
Once monthly for the first 3 months, then once every 3 months as ongoing maintenance.
Onset
3–6 months
Meaningful results typically become apparent over 3–6 months. Maximum benefit accumulates with ongoing treatment over 12–24 months.
Commitment
Ongoing
Androgenetic alopecia is a chronic condition. Ongoing periodic treatment is required to maintain results.
Side effects and considerations
The systemic side effects associated with oral dutasteride — reduced libido, erectile dysfunction, reduced ejaculate volume, and mood changes — are driven by whole-body DHT suppression. By delivering dutasteride intradermally into the scalp rather than orally, systemic absorption and the accompanying hormonal disruption are substantially reduced. This is a central reason I prefer the injectable route.
Injection-site discomfort, temporary redness, and minor swelling are possible and typically short-lived. As with any intradermal injection, there is a small risk of bruising or localised tenderness.
Dutasteride remains absolutely contraindicated in pregnancy and in women of childbearing potential due to the risk of feminisation of a male foetus, regardless of the route of administration. Female patients must be post-menopausal or using reliable contraception.