Dutasteride is a prescription oral medication, licensed for an enlarged prostate, that blocks both forms of the enzyme making the hormone behind inherited pattern hair loss. Short trials show more and thicker hair than placebo, and more than the older licensed medication at six months; almost all the evidence stops there. The same hormone block brings reduced sexual function, lower semen quality, breast changes and distorted prostate cancer screening. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Prostate-specific antigen | Below 1.0 ng/mL under age 60; thereafter track rises from the on-treatment low point | Detects prostate cancer despite drug-induced suppression |
| Total testosterone | 600–900 ng/dL | Rises as conversion to dihydrotestosterone is blocked; confirms the expected hormonal shift |
| Dihydrotestosterone | No established on-treatment target; track the fall from the pre-treatment value, expected above 90% | Confirms absorption and adequate enzyme blockade |
| Oestradiol | 20–30 pg/mL | Breast tenderness and gynaecomastia track a rising oestrogen-to-androgen ratio |
| Ferritin | 70–100 ng/mL | Low iron stores cause diffuse shedding that no androgen blocker will correct |
| 25-hydroxyvitamin D | 40–60 ng/mL | Deficiency is associated with disordered hair cycling |
| Thyroid-stimulating hormone | 0.5–2.0 mIU/L | Thyroid dysfunction produces shedding that mimics treatment failure |
| Alanine aminotransferase | Below 25 U/L in men, below 20 U/L in women | Clearance is hepatic, so impairment raises drug exposure |
| Semen analysis | At least 39 million total sperm and 40% motility | Establishes a pre-treatment baseline where fatherhood is planned |
Cadence: Baseline before the first capsule; hormones and prostate-specific antigen repeated at 6 months, then every 12 months. Photography at 6 and 12 months, then annually.