Skip to main content

Finasteride (Monograph)

Brand names: Propecia, Proscar
Drug class: 5-alpha-Reductase Inhibitors
- Hair Growth Stimulants
VA class: HS900
Chemical name: (5α,17β)-N-(1,1-dimethylethyl)-3-oxo-4-azaandrost-1-ene-17-carboxamide
CAS number: 98319-26-7

Medically reviewed by on Jan 23, 2023. Written by ASHP.


Specific inhibitor of steroid 5α-reductase; blocks conversion of testosterone by type 2 5α-reductase to 5α-dihydrotestosterone (DHT).

Uses for Finasteride

Benign Prostatic Hypertrophy (BPH)

Treatment of symptomatic BPH to improve symptoms and reduce the risk of acute urinary retention and the need for surgery. Ineffective in patients who do not have evidence of prostatic enlargement.

Used alone or in combination with an α1-adrenergic blocking agent (e.g., doxazosin). Combination therapy with a 5α-reductase inhibitor and an α1-blocker has been more effective than therapy with either drug alone in preventing long-term BPH symptom progression. Men at risk for BPH progression are most likely to benefit from combination therapy.

Steroid 5α-reductase inhibitors may be a useful alternative to surgery in patients with obstructive manifestations who are awaiting or unwilling to undergo surgical correction of BPH; may aid those who are at increased risk from or are not candidates for prostate surgery. Also may be considered in patients who have symptomatic prostatic enlargement but whose symptoms are not bothersome (i.e., do not interfere with activities of daily living) in order to prevent progression of the disease.

Although drug therapy usually is not as effective as surgical therapy, it may provide adequate symptomatic relief with fewer and less serious adverse effects compared with surgery.

Androgenetic Alopecia

Stimulates regrowth of hair in men with mild to moderate androgenetic alopecia (male pattern alopecia, hereditary alopecia, common male baldness).

Effective in promoting hair regrowth in young and middle-aged men (18–41 years of age) with mild to moderate androgenetic alopecia and hair loss on the vertex of the scalp and/or anterior mid-scalp area; the effects on bitemporal recession are not established.

Recommended only for use in men; not indicated for use in women or children. Ineffective for treatment of hair loss in postmenopausal women with androgenetic alopecia.

Withdrawal of the drug leads to reversal of clinical benefit within 1 year. Therapy must be continued to sustain initial regrowth and subsequent slowing of hair loss. Maximum improvement in hair count occurs during first 2 years of therapy.

Finasteride Dosage and Administration


Administer orally without regard to meals.




5 mg once daily, alone or in combination with doxazosin mesylate.

While early symptomatic improvement may occur, ≥6 months of therapy may be necessary to determine clinical benefit.

Androgenetic Alopecia

1 mg once daily.

Generally administered for ≥3 months before benefit is observed. If improvement does not occur within 1 year, further treatment with the drug is unlikely to provide benefit.

Continued use recommended to sustain benefit, which should be re-evaluated periodically.

Discontinuance leads to reversal of effect within 12 months.

Special Populations

Hepatic Impairment

No specific dosage recommendations for hepatic impairment. (See Hepatic Impairment under Cautions.)

Renal Impairment

Dosage adjustment not required.

Geriatric Patients

Dosage adjustment not required.

Cautions for Finasteride


  • Known or suspected pregnancy. (See Fetal/Neonatal Morbidity and also Pregnancy under Warnings/Precautions.)

  • Known hypersensitivity to finasteride or any ingredient in the formulation.


Fetal/Neonatal Morbidity

May cause fetal harm; teratogenicity demonstrated in animals.

Animal studies indicate adverse effects on embryofetal development of male fetuses exposed to the drug during pregnancy (e.g., abnormalities of the external genitalia, decreased prostatic and seminal vesicular weights, delayed preputial separation, transient nipple development).

No abnormalities were observed in female offspring exposed to any finasteride dosage in utero.

Because of the potential for absorption through the skin and the subsequent potential risk to a male fetus, pregnant women or women who potentially may be pregnant should avoid direct contact with broken (e.g., crushed) tablets of the drug. If such contact occurs, wash affected area immediately with soap and water.

If used during pregnancy or if pregnancy occurs, apprise the pregnant woman of potential fetal hazard to the male fetus.

Patient Assessment

Evaluate candidates for finasteride therapy for other urologic conditions that might mimic BPH, such as infection, prostate cancer, stricture disease, hypotonic bladder, other neurogenic disorders.

Perform digital rectal examinations, as well as other screening tests for prostate cancer (e.g., serum prostate-specific antigen [PSA] concentration), before initiating therapy for BPH and periodically thereafter. (See Prostate-specific Antigen under Cautions and also see Specific Drugs and Laboratory Tests under Interactions.)

Monitor patients with a large residual urinary volume and/or severely diminished urinary flow carefully for obstructive uropathy. Such patients may not be candidates for finasteride therapy.

High-grade Prostate Cancer

5α-Reductase inhibitors may increase risk of development of high-grade prostate cancer.

In 2 placebo-controlled trials evaluating finasteride (5 mg daily for 7 years) or dutasteride (0.5 mg daily for 4 years) for prevention of prostate cancer, overall occurrence of prostate cancer was reduced (due to reduction in lower-grade tumors) but incidence of high-grade tumors (Gleason score 8–10) was increased in men receiving finasteride or dutasteride. Not known whether detection bias (e.g., drug-induced reduction in prostate volume might have aided biopsy detection) or study-related factors influenced results.

Not FDA-labeled for prevention of prostate cancer.

Prostate-specific Antigen

Decreases PSA concentrations; may interfere with interpretation of serum PSA determinations. (See Specific Drugs and Laboratory Tests under Interactions.)

May decrease serum PSA concentrations in men with prostate cancer; however, clinical benefit from this effect has not been demonstrated.

Carefully evaluate any confirmed increase in serum PSA concentration during therapy, even if PSA value is within normal range for men not receiving 5α-reductase inhibitor therapy.

Noncompliance may affect PSA concentrations; consider when evaluating test results.

Breast Neoplasia

Breast cancer reported in several men receiving finasteride 5 mg daily (alone or in combination with doxazosin) and several placebo recipients in long-term trials of finasteride. Also reported during postmarketing experience in men receiving finasteride 1 mg daily. Not known whether a causal relationship exists between long-term finasteride use and breast neoplasia in men.

Specific Populations


Category X. (See Fetal/Neonatal Morbidity and also see Contraindications under Cautions.)


Not known whether finasteride is distributed into milk, but the drug is not indicated for use in women.

Pediatric Use

Safety and efficacy not established, but the drug is not indicated for use in children.

Geriatric Use

No substantial differences in safety and efficacy for treatment of BPH in men ≥65 or ≥75 years of age relative to younger men. Efficacy for promoting hair regrowth in geriatric men with androgenetic alopecia not established.

Hepatic Impairment

Not studied in patients with hepatic impairment. Extensively metabolized in the liver. Use with caution.

Common Adverse Effects

Impotence, decreased libido, ejaculation disorder (e.g., decreased volume of ejaculate), breast enlargement.

Interactions for Finasteride

Extensively metabolized by CYP3A4; apparently does not affect CYP isoenzymes.

Specific Drugs and Laboratory Tests

Drug or Test




Pharmacokinetic or pharmacodynamic interaction unlikely


Pharmacokinetic or pharmacodynamic interaction unlikely


Pharmacokinetic or pharmacodynamic interaction unlikely

Test for PSA

50% decrease in serum PSA concentration in patients with BPH receiving 5 mg daily, even in those with prostate cancer

PSA decreased from 0.7 ng/mL at baseline to 0.5 ng/mL at 12 months with 1-mg daily dosage for androgenetic alopecia

No substantial change in ratio of free to total PSA (percentage of free PSA)

Do not interpret decrease in PSA value as a therapeutic effect on prostate cancer

Take decrease into account for interpretation of PSA values in men receiving finasteride

For interpretation of serial PSAs in men with BPH receiving finasteride 5 mg daily, establish new baseline PSA ≥6 months after initiation of treatment

For clinical interpretation of PSA values in men with BPH receiving finasteride 5 mg daily for ≥6 months, double the reported PSA value for comparison with normal values in men not receiving the drug

No adjustment of reported values of ratio appears to be required


Pharmacokinetic or pharmacodynamic interaction unlikely


Pharmacokinetic or pharmacodynamic interaction unlikely

Finasteride Pharmacokinetics



Mean bioavailability is 63–65%.


Rapid, with maximum decrease in serum DHT concentrations at 8 hours following oral administration of first dose of 5 mg, and 65% suppression of serum DHT within 24 hours after oral administration of 1 mg.


DHT suppression maintained throughout 24-hour dosage interval; DHT decreased by about 70% with 5-mg daily dosage for at least 4 years.


Food does not appear to affect absorption.



Crosses blood-brain barrier, but is not preferentially distributed into CSF.

Distributed into semen in amounts estimated to be 50- to 100-fold less than the dose (5 mcg) that had no effect on circulating DHT concentrations in men.

Crosses the placenta in rats.

Not known whether distributed into human milk.

Plasma Protein Binding

Approximately 90%.



Extensively metabolized, principally in the liver, via CYP3A4; 2 metabolites identified with ≤20% of activity of finasteride.

Elimination Route

Principally excreted in the feces (57%) and in urine (39%) as metabolites.


Males 18–60 years of age: 5–6 hours.

Special Populations

Half-life in males ≥70 years of age: 8 hours; increase not clinically important.

Effect of hepatic impairment on pharmacokinetics not studied; extensively metabolized in the liver.

In patients with chronic renal impairment (Clcr 9–55 mL/minute), pharmacokinetics after single-dose administration appear to be similar to those in healthy individuals except that the proportion excreted in feces versus urine is increased in those with impairment.





5-mg tablets: Tight, light resistant containers at room temperature <30°.

1-mg tablets: Tight, light resistant containers at 15–30°C.


  • Competitive specific inhibitor of type 2 isoenzyme of steroid 5α-reductase.

  • 100-fold more selective for type 2 5α-reductase than for type 1 isoenzyme; chronic treatment may have some effect on the type 1 isoenzyme.

  • Type 2 steroid 5α-reductase isoenzyme converts testosterone to DHT in the prostate gland, seminal vesicles, epididymides, liver, and the inner root sheath of hair follicles and is responsible for the formation of about two-thirds of circulating DHT.

  • Reduces serum and tissue (e.g., prostate, scalp) DHT concentrations substantially.

  • Increases serum testosterone concentrations minimally to moderately (usually within the normal range) and prostatic testosterone concentrations substantially.

  • Decreases prostatic volume by an average of about 20–30% after 6–24 months of continued therapy in most patients with BPH.

  • In men with androgenetic alopecia, decreases scalp DHT concentrations to levels found in hairy scalp, reduces serum DHT, increases hair regrowth, and slows hair loss. However, exact mechanism of action not fully elucidated.

Advice to Patients

  • Importance of obtaining and reading patient information on finasteride before initiation of therapy and with each new prescription refill.

  • Importance of informing patients that finasteride decreases serum PSA concentrations. Importance of appropriate medical evaluation of any increase in PSA concentration. If a PSA test is performed, importance of patient informing the clinician that he is taking a 5α-reductase inhibitor.

  • Importance of informing patients that the incidence of high-grade prostate cancer was increased in men receiving 5α-reductase inhibitors (including finasteride) in clinical trials evaluating efficacy of these drugs for prostate cancer prevention.

  • Risk to male fetuses. Importance of advising patients that pregnant women or women who may be pregnant should avoid direct contact with broken or crushed tablets of the drug; if such contact occurs, wash affected area immediately with soap and water and inform clinician. (See Fetal/Neonatal Morbidity under Cautions.)

  • Advise patients that a decrease in the volume of ejaculate may occur but that this does not appear to interfere with normal sexual function.

  • Advise patients of the possibility of impotence and decreased libido.

  • Importance of promptly informing clinician of any changes in breasts (e.g., lumps, pain, nipple discharge), since breast changes (enlargement, tenderness, neoplasm) have been reported.

  • Advise that ≥6 months of continuous therapy may be required before improvement in BPH symptoms occurs and a decrease in prostate size may not noticeably improve urine flow or symptoms.

  • Advise that ≥3 months of continuous therapy may be required before improvement in androgenetic baldness occurs, and if no improvement is observed after 12 months, further treatment is unlikely to be of benefit.

  • Advise that hair growth gained during treatment for androgenetic baldness will likely be lost within 12 months after discontinuing the drug.

  • Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs, as well as any concomitant illnesses.

  • Importance of advising patients of other important precautionary information. (See Cautions.)


Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name



Dosage Forms


Brand Names



Tablets, film-coated

1 mg

Propecia (available in regular and Pro-Pak)


5 mg*

Finasteride Tablets



AHFS DI Essentials™. © Copyright 2023, Selected Revisions February 2, 2012. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

Reload page with references included