Finasteride Dosage UK: 1 mg & 5 mg Guide

Posology based on the MHRA-approved Summary of Product Characteristics (SmPC) for Propecia (1 mg) and Proscar (5 mg). | Back to UK hub

MHRA-approved dosing

Indication	Brand (UK)	MHRA-approved dose	Route	Frequency
Androgenetic alopecia (AGA)	Propecia / generic 1 mg	1 mg	Oral	Once daily
Benign prostatic hyperplasia (BPH)	Proscar / generic 5 mg	5 mg	Oral	Once daily

Source: MHRA-approved SmPCs for Propecia and Proscar (eMC, 2024). No dose adjustment required for renal impairment. Dose reduction not required in elderly patients.

Finasteride 1 mg: hair loss (AGA)

Dose: 1 mg by mouth, once daily
With or without food: Either; food does not affect bioavailability
Best time: No evidence for a specific time of day; consistency is more important than timing. See time of day guide.
Duration: Indefinite. Hair loss returns to pre-treatment baseline within 6-12 months of stopping
Minimum trial period: 6-12 months before assessing response per NICE CKS and MHRA SmPC

Finasteride 5 mg: BPH

Dose: 5 mg by mouth, once daily
NHS prescribable: Yes, on FP10; NICE CG97 recommends it for men with a prostate over 30 g or PSA above 1.4 ng/mL at high risk of progression
Expected response: Maximum prostate volume reduction (20-30%) at 6-12 months; symptom improvement (IPSS) typically evident at 3-6 months
Combination with alpha-blocker: NICE CG97 advises considering combination therapy (finasteride + alpha-blocker) for men with bothersome moderate-to-severe LUTS and a prostate over 30 g or PSA above 1.4 ng/mL

Missed dose

The MHRA SmPC does not provide explicit missed-dose guidance. Based on finasteride’s pharmacokinetics (half-life 5-6 hours; DHT suppression maintained for days): if you miss a dose, take it as soon as you remember on the same day. If you only remember the next day, skip the missed dose and resume normal dosing. Do not take a double dose.

Special populations (MHRA contraindications)

Population	MHRA guidance
Women, pregnant or of childbearing potential	Contraindicated. Finasteride may cause abnormalities of the external genitalia of a male foetus. Women must not handle crushed tablets.
Children / adolescents under 18	Not licensed. No data.
Renal impairment	No dose adjustment required.
Hepatic impairment	Use with caution, no data for severe hepatic impairment. Not recommended if significantly impaired liver function.
Elderly (>70 years)	No dose adjustment required; pharmacokinetics not significantly altered.

Source: MHRA-approved Propecia and Proscar SmPCs (eMC, 2024).

PSA monitoring note for UK prescribers

Clinical note for UK GPs and urologists: Finasteride 5 mg reduces serum PSA by approximately 50% after 6 months of use. Any measured PSA in a patient on finasteride should be multiplied by 2.0 (for 5 mg) or 1.7 (for 1 mg) to derive the equivalent untreated PSA. Do not instruct patients to stop finasteride before PSA testing, the correction formula is more reliable. Source: BAUS guidance; MHRA Proscar SmPC.

Sources: MHRA Propecia SmPC (eMC, 2024). MHRA Proscar SmPC (eMC, 2024). NICE CG97: Lower urinary tract symptoms in men (2010, updated 2015). Kaufman KD et al. JAAD 1998.