Oral minoxidil, an old prescription blood-pressure medication, is used at very low doses to regrow scalp hair. In hereditary thinning the tablet regrows hair about as well as the approved scalp solution, without scalp residue or irritation. Gains last only while continued. Unwanted facial and body hair is the most common side effect; fluid around the heart is rare at these doses, though evidence conflicts. The evidence base is moderate. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Blood pressure (seated and standing) | 110–120 / 70–80 mmHg; standing drop <20 mmHg systolic | Detects low blood pressure |
| Resting heart rate | 55–75 beats per minute | Detects reflex rise in heart rate |
| Body weight | Within 1 kg of baseline | Early sign of fluid retention |
| Kidney function (creatinine, eGFR) | eGFR >90 mL/min/1.73 m² | Drug clearance and risk of fluid around the heart |
| Potassium | 4.0–4.5 mmol/L | Safety with spironolactone or diuretics |
| Ferritin | 70–150 ng/mL | Rules out iron-related shedding |
| Thyroid-stimulating hormone | 1.0–2.5 mIU/L | Rules out thyroid-related hair loss |
| 25-hydroxyvitamin D | 40–60 ng/mL | Deficiency linked to hair loss |
| Pregnancy test (hCG) | Negative | Avoids fetal exposure |
| Electrocardiogram | Normal heart rhythm | Baseline for heart symptoms; only if cardiac history or symptoms |
| Scalp hair density (photographs or phototrichogram) | No established target; track change from own baseline | Defines success |
Cadence: Baseline testing before starting (electrocardiogram only with heart disease, palpitations or major cardiac risk factors); home blood pressure and pulse 1–2 weeks after starting and after each dose change; weekly weight for the first 3 months; clinical review at 3 months, then every 6 months with repeat photographs; kidney function and potassium every 6–12 months (at 3 months with spironolactone or kidney disease)