Finasteride
Selective inhibitor of type II 5-alpha-reductase. FDA-approved for androgenetic alopecia (Propecia 1 mg) and BPH (Proscar 5 mg). Reduces DHT formation by ~70%.
Related comparisons
Finasteride vs DutasterideWHAT IS FINASTERIDE?
Detailed overview
Finasteride is a synthetic 4-azasteroid developed by Merck (Proscar for BPH, FDA 1992; Propecia for alopecia, FDA 1997). It is a selective inhibitor of the type II 5-alpha-reductase enzyme, blocking the conversion of testosterone to dihydrotestosterone (DHT) in the prostate and hair follicles. DHT is the primary driver of hair follicle miniaturization (androgenetic alopecia) and prostate growth (BPH). According to the Kaufman 1998 RCT (PMID 9591820), at 24 months hair growth was documented in 48% of alopecia patients and hair stabilization in 90%. According to the Roehrborn 2002 MTOPS trial (NEJM PMID 12944571), it reduces BPH progression by 39% as monotherapy. The difference between ATC codes D11AX10 (alopecia 1 mg) and G04CB01 (BPH 5 mg) is only the dose and the indication.
ATC code
D11AX10 (1mg) / G04CB01 (5mg)
Prescription status
Prescription only (Rx)
Mechanism of action
Selective inhibition of type II 5-alpha-reductase, ~70% DHT reduction
Half-life
5-6 hours plasma, 96+ hours enzyme affinity
Onset of action
3-6 months (hair stabilization), 6-12 months (regrowth)
Data console
Lab data
Safety
Side effects, stop signs, contraindications
Side effects · 7
- Sexual side effects: decreased libido (~1.8%), erectile dysfunction (~1.3%), ejaculation disorder and reduced ejaculate volume (~1%); usually reversible after discontinuation.
- Mood disorders: depression, anxiety and (rarely) suicidal ideation reported; the FDA label warns of this, discontinue and seek medical advice if psychiatric symptoms occur.
- Breast changes: gynaecomastia (breast enlargement), breast tenderness and pain; rarely a breast lump, pain or nipple discharge that must be evaluated (male breast cancer rarely reported).
- PSA decreases by ~50%: prostate-specific antigen becomes falsely low, so during prostate cancer screening the measured PSA must be doubled to avoid a false negative.
- Hypersensitivity and skin reactions: rash, pruritus, urticaria, swelling of the lips and face (angioedema); rarely an allergic reaction requiring immediate discontinuation.
- Slightly increased incidence of high-grade prostate cancer (Gleason 8-10) in the PCPT trial, while overall prostate cancer risk fell; with no difference in overall survival.
- Disputed persistent (post-finasteride) symptoms: sexual, mood and cognitive complaints persisting after stopping in a small fraction; clinically debated but listed in the patient information.
Contraindications · 3
- Pregnancy (FDA category X)
- Women of childbearing age
- Hypersensitivity
Related Hair & Skin
Same therapeutic category
Studies
Related research and clinical findings
Progression of hair loss in men with androgenetic alopecia (male pattern hair loss): long-term (5-year) controlled observational data in placebo-treated patients.
Kaufman KD, Girman CJ, Round EM, Johnson-Levonas AO, Shah AK, Rotonda J
The long-term effect of doxazosin, finasteride, and combination therapy on the clinical progression of BPH (MTOPS)
McConnell JD, Roehrborn CG, Bautista OM et al.
The influence of finasteride on the development of prostate cancer (PCPT)
Thompson IM, Goodman PJ, Tangen CM et al.
The Risk of Benign Prostatic Hyperplasia and Prostate Cancer With Long-Term, Low Dose Finasteride Use in Adult Men with Nonscarring Alopecia.
Adler R, Kozlov M, Viola J
Effectiveness and Safety of Topical Finasteride for Male Androgenetic Alopecia: Real World Data.
Piraccini BM, Rapparini L, Quadrelli F
Adverse effects and safety of 5-alpha reductase inhibitors (finasteride, dutasteride)
Hirshburg JM, Kelsey PA, Therrien CA et al.
Persistent sexual side effects of finasteride (post-finasteride syndrome)
Irwig MS, Kolukula S.
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Educational hair and skin info from official sources (PubMed, FDA, EMA). Does NOT replace medical consultation. Talk to a dermatologist!
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