Benign prostatic hyperplasia agents · Genitourinary
Finasteride
Proscar® · Propecia®(brand names vary by market)
Shrinks the prostate over months, and halves the PSA while doing it.
Mechanism
Inhibits 5-alpha reductase, blocking conversion of testosterone to dihydrotestosterone: the prostate shrinks over months and scalp hair follicles are protected.
Indications
- Benign prostatic hyperplasia with an enlarged gland
- Androgenetic alopecia at lower doses
Formulations
Dosing concepts
Time to effect
Three to six months before symptomatic benefit, which is why it is combined with an alpha blocker when symptoms need relief now.
Gland size matters
It only helps when the prostate is genuinely enlarged; in a small gland it offers little.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~65%
- Half-life
- 5 to 6 h in adults, longer in older men
- Elimination
- hepatic: CYP3A4
- Protein binding
- ~90%
Adverse effects
- Reduced libido and erectile dysfunctioncommonUsually reversible; a persistent syndrome after stopping is reported and remains debated.
- Gynecomastiacommon
- Reduced ejaculate volumecommon
- Depressionserious
Contraindications & precautions
Contraindications
- Pregnancy: it must not be handled by anyone who is or may become pregnant
- Children
Precautions
- PSA interpretation
- Mood disorder
- Blood donation, which is deferred during therapy
Interactions
No curated interaction entries yet for this agent.
Monitoring
PSA, doubled before interpretation
It halves the value; forgetting that has delayed cancer diagnoses · Establish a new baseline after 6 months
Symptom score and gland size
Efficacy
Mood and sexual function
Common reasons for stopping, and worth asking about directly
Counselling points
- It takes three to six months to work.
- Women who are or could become pregnant must not handle broken or crushed tablets.
- It changes your PSA result; make sure any doctor checking it knows you take this.
- Tell us about changes in sexual function or mood.
Clinical pearls
- A PSA on finasteride is doubled before it is interpreted. This is one of the clearest examples of a drug changing the meaning of a test rather than the patient's physiology.
- It is teratogenic through skin contact with a broken tablet, which is why the handling advice is about the household rather than only the patient.
References & review
- Finasteride product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.