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Medically reviewed by Last updated on May 20, 2019.


(fi NAS teer ide)

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Tablet, Oral:

Propecia: 1 mg

Proscar: 5 mg [contains fd&c blue #2 aluminum lake]

Generic: 1 mg, 5 mg

Brand Names: U.S.

  • Propecia
  • Proscar

Pharmacologic Category

  • 5 Alpha-Reductase Inhibitor


Finasteride competitively inhibits type II 5-alpha reductase, resulting in inhibition of the conversion of testosterone to dihydrotestosterone and markedly suppresses serum dihydrotestosterone levels


Vdss: 76 L


Hepatic (extensive) via CYP3A4; two active metabolites (<20% activity of finasteride)


Feces (57%) and urine (39%; as metabolites)

Time to Peak

Serum: 1 to 2 hours

Duration of Action

Dihydrotestosterone levels return to normal within 14 days of discontinuation of treatment; BPH: Prostate volume returns to baseline within ~3 months after discontinuation; Male pattern baldness: Reversal of increased hair count within 12 months

Half-Life Elimination

5 to 6 hours (range: 3 to 16 hours); Elderly (≥70 years): 8 hours (range: 6 to 15 hours)

Protein Binding


Special Populations: Renal Function Impairment

Urinary excretion of metabolites was decreased in patients with renal impairment. This decrease was associated with an increase in fecal excretion of metabolites. Plasma concentrations of metabolites were significantly higher in patients with renal impairment (based on a 60% increase in total radioactivity AUC).

Special Populations: Elderly

Mean AUC0-24 increases 15%.

Use: Labeled Indications

Androgenetic alopecia (Propecia): Treatment of male pattern hair loss in men only.

Limitations of use: Efficacy in bitemporal recession has not been established; not indicated for use in women.

Benign prostatic hyperplasia (Proscar): Treatment (monotherapy) of symptomatic benign prostatic hyperplasia (BPH) to improve symptoms, reduce the risk of acute urinary retention, and to reduce the risk of need for BPH-related surgery); used in combination with an alpha-blocker (doxazosin) to reduce the risk of symptomatic progression.

Limitations of use: Not approved for the prevention of prostate cancer.

Off Label Uses


Data from a systematic review and network meta-analysis of published randomized trials of adult females with hirsutism (including idiopathic hirsutism and hirsutism in women with polycystic ovary syndrome or nonclassic congenital adrenal hyperplasia) support the use of finasteride for treatment of hirsutism [Barrionuevo 2018]. Additional trials may be necessary to further define the role of finasteride for the treatment of this condition.

Based on the Evaluation and Treatment of Hirsutism in Premenopausal Women: An Endocrine Society Clinical Practice guideline, finasteride is effective and may be considered among other antiandrogens in the management of this condition. Finasteride may be considered for initial therapy, either as monotherapy in women who are not at risk for becoming pregnant, or in combination with an oral contraceptive in select women with severe hirsutism causing distress and/or a prior history of inadequate response to oral contraceptive therapy. Finasteride may also be considered for add-on therapy in women who fail to achieve a satisfactory response to initial oral contraceptive monotherapy [Martin 2018].


Hypersensitivity to finasteride or any component of the formulation; pregnancy or women of childbearing potential

Dosing: Adult

Benign prostatic hyperplasia (Proscar): Males: Oral: 5 mg once daily (either as a single agent or in combination with doxazosin); early responses may occur although 6 months of treatment is usually needed to assess benefit.

Hirsutism (off-label use): Females: Oral: 2.5 to 5 mg once daily; assess response at 6-month intervals before adjusting dose, adding additional agents, or switching to alternative therapy (Endocrine Society [Martin 2018]).

Male pattern baldness (Propecia): Males: Oral: 1 mg once daily; may take 3 months or longer of daily use for observed benefit; continued use is recommended to sustain benefit.

Dosing: Geriatric

Refer to adult dosing.


May be administered with or without meals. Females of childbearing age should not touch or handle crushed or broken tablets.


Propecia: Store at 15°C to 30°C (59°F to 86°F). Keep container tightly closed and protect from moisture.

Proscar: Store below 30°C (86°F). Protect from light. Keep container tightly closed.

Drug Interactions

There are no known significant interactions.

Test Interactions

PSA levels decrease in treated patients. After 6 months of therapy, PSA levels stabilize to a new baseline that is ~50% of pretreatment values. If following serial PSAs in a patient, re-establish a new baseline after ≥6 months of use.

Adverse Reactions

>10%: Genitourinary: Impotence (monotherapy 5% to 19%)

1% to 10%:

Cardiovascular: Orthostatic hypotension (monotherapy 9%), peripheral edema (monotherapy 1%), hypotension (monotherapy 1%)

Endocrine & metabolic: Decreased libido (monotherapy 2% to 10%), gynecomastia (monotherapy 1% to 2%)

Genitourinary: Ejaculatory disorder (monotherapy <1% to 7%), decreased ejaculate volume (monotherapy 2% to 4%), sexual disorder (3%), breast tenderness (monotherapy ≤1%)

Hematologic & oncologic: Prostate cancer (high grade: 2%)

Respiratory: Rhinitis (monotherapy 1%)

<1%, postmarketing, and/or case reports: Altered mental status, attempted suicide (Welk 2017), breast hypertrophy, change in libido, depression, hypersensitivity reaction, male infertility (temporary), malignant neoplasm of the breast (men), suicidal ideation (Welk 2017), testicular pain


Disease-related concerns:

• Diminished urinary flow: Carefully monitor patients with a large residual urinary volume or severely diminished urinary flow for obstructive uropathy; these patients may not be candidates for finasteride therapy.

• Hepatic impairment: Use with caution in patients with hepatic impairment; finasteride is extensively metabolized in the liver.

• Prostate cancer: When compared to placebo, 5-alpha-reductase inhibitors (5-ARIs) have been associated with an increase in the incidence of high-grade prostate cancers; 5-ARIs are not approved in the US or Canada for the prevention of prostate cancer.

Special handling:

• Females/pregnancy: Active ingredient of crushed or broken tablets can be absorbed through the skin; unbroken tablets are coated which prevents contact with the active ingredient during normal handling. Pregnant females should avoid contact with crushed or broken tablets; finasteride may negatively impact fetal development.

Other warnings/precautions:

• Appropriate use: Other urological diseases (including prostate cancer) should be ruled out before initiating (in BPH management). Not indicated for use in pediatric patients.

• Duration of therapy: For BPH, a minimum of 6 months of treatment may be necessary to determine whether an individual will respond to finasteride; for male pattern hair loss, daily use for 3 months or longer may be required before benefit is observed (withdrawal of treatment leads to reversal of hair growth effect within 12 months).

• PSA monitoring: Reduces prostate specific antigen (PSA) concentration by ~50% within 6 months of treatment. To interpret serial PSAs, a new PSA baseline should be established ≥6 months after treatment initiation and PSA monitored periodically thereafter. A confirmed PSA increase while on this medication, even if within normal limits, may be associated with an increased risk for prostate cancer and should be evaluated. Finasteride does not interfere with free PSA levels.

Monitoring Parameters

To interpret serial PSAs, establish a new PSA baseline ≥6 months after treatment initiation and monitor PSA periodically thereafter. Objective and subjective signs of relief of benign prostatic hyperplasia, including improvement in urinary flow, reduction in symptoms of urgency, and relief of difficulty in micturition.

Pregnancy Risk Factor


Pregnancy Considerations

Use is contraindicated in females of childbearing potential.

Abnormalities of external male genitalia were reported in animal reproduction studies. Pregnant females are advised to avoid contact with crushed or broken tablets.

Adequate contraception is recommended if used off-label in the management hirsutism in females associated with PCOS (ACOG 194 2018).

Patient Education

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience sexual dysfunction, loss of strength and energy, or decreased libido. Have patient report immediately to prescriber enlarged breasts, severe dizziness, passing out, depression, testicle pain, lump in breast, breast soreness or pain, or nipple discharge (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.