Before starting
Required
- Baseline
- Digital rectal exam
After starting
Required
- At 6 months
- Prostate specific antigen 5α-reductase inhibitors reduce concentrations by approximately 50% after 6 months of treatment. The prostate specific antigen (PSA) level at 6 months should be regarded as the new baseline. For comparison with normal PSA ranges in untreated men, the measured PSA value should be doubled.
Ongoing once stable
Required
- Periodically
- Prostate specific antigen
- Digital rectal exam
Abnormal results
Prostate specific antigen (PSA)
Any confirmed rise in PSA from the lowest level reached during 5α-reductase inhibitor treatment may indicate prostate cancer or non-adherence. The rise should be carefully evaluated, even if PSA remains within the normal range for untreated individuals. The PSA should be doubled for comparison with normal ranges for untreated men.
Notes
An MHRA Drug Safety Update advises patients to contact a healthcare professional if they experience suicidal thoughts, depression, or sexual dysfunction.
Bibliography
- Electronic Medicines Compendium (emc). Proscar 5 mg Film-Coated Tablets Summary of Product Characteristics. Datapharm Ltd. Available at: https://www.medicines.org.uk/emc/product/1008/smpc [cited 28/10/2026].
- Electronic Medicines Compendium (emc). Avodart 0.5 mg Soft Capsules Summary of Product Characteristics. Datapharm Ltd. Available at: https://www.medicines.org.uk/emc/product/6758/smpc [cited 28/10/2026].
- Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press [cited 28/10/2026].
- National Institute for Health and Care Excellence (NICE). Lower urinary tract symptoms (LUTS) in men: 5-alpha reductase inhibitors. Clinical Knowledge Summaries. NICE. Available at: https://cks.nice.org.uk/topics/luts-in-men/prescribing-information/5-alpha-reductase-inhibitors/ [cited 28/10/2026].
- Medicines and Healthcare products Regulatory Agency (MHRA). Finasteride and Dutasteride – updated safety warnings for psychiatric side effects and sexual dysfunction. Drug Safety Update. 11 May 2026. Available at: https://www.gov.uk/drug-safety-update/finasteride-and-dutasteride-updated-safety-warnings-for-psychiatric-side-effects-and-sexual-dysfunction [cited 28/10/2026].