Finasteride

Category: hormone

Aliases: Propecia, Proscar, MK-906

Pharmacological Mechanism

4-Azasteroid competitive inhibitor of 5α-reductase type II (dominant in prostate, seminal vesicles, scalp follicles). Blocks conversion of testosterone → dihydrotestosterone (DHT). ~70% serum DHT suppression at 1 mg/d; higher suppression at 5 mg in prostatic tissue. Does not affect testosterone or estradiol levels. Does not cover type I isoform (sebum, liver) — dutasteride inhibits both.

Half-Life (t½)

PO: 6h

Dosing Guidelines

• PO: Typical 1 mg (Range: 1–1 mg)

Target Organ Systems

• endocrine
• reproductive
• integumentary

Interactions

• Testosterone (TRT) (synergistic): TRT + finasteride used off-label to blunt DHT-mediated scalp/prostate effects without sacrificing AR-driven benefits. [Gormley 1995]
• Dutasteride (warn): alternative 5α-reductase inhibitor — don't combine, therapeutic redundancy

Pathways It Modulates

• Androgenetic alopecia (inhibitor) — SRD5A2 — oral 1 mg AGA mainstay; ↓DHT 60–70%
• Hypothalamic-pituitary-gonadal axis (inhibitor) — 5α-reductase type 2
• Progesterone receptor signaling (inhibitor) — 5α-reductase → ↓allopregnanolone (post-finasteride syndrome mechanism?)

Chemical Identifiers

• PubChem CID: 57363
• Formula: C23H36N2O2
• Molecular weight: 372.55 g/mol
• InChIKey: DBEPLOCGEIEOCV-WSBQPABSSA-N
• SMILES: C[C@]12CC[C@H]3[C@H]([C@@H]1CC[C@@H]2C(=O)NC(C)(C)C)CC[C@@H]4[C@@]3(C=CC(=O)N4)C

References

• PMID 8846625
• PMID 8562856
• PMID 9605412
• PMID 19922895