Skip to Content


Medically reviewed by Last updated on Sep 2, 2020.


(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 (male pattern hair loss): Treatment of male pattern hair loss in men.

Limitations of use: Efficacy in bitemporal recession has not been established.

Benign prostatic hyperplasia: Treatment (monotherapy) of symptomatic benign prostatic hyperplasia (BPH) to improve symptoms, reduce the risk of acute urinary retention, and 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 women with hirsutism (idiopathic, related to polycystic ovary syndrome or nonclassic congenital adrenal hyperplasia) support the use of finasteride for treatment of hirsutism [Barrionuevo 2018].

Based on the Endocrine Society clinical practice guideline on the evaluation and treatment of hirsutism in premenopausal women, 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 [Endocrine Society [Martin 2018]].


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

Dosing: Adult

Androgenetic alopecia (male pattern hair loss): Males: Oral: 1 mg once daily. Continue for at least 12 months to assess full effect; continued daily use is required to sustain benefit (Donovan 2019; Leyden 1999; Whiting 1999).

Benign prostatic hyperplasia (alternative agent): Note: Reserve use for patients with significantly enlarged prostates, those intolerant of or refractory to alpha-1 adrenergic antagonists, or those with hematuria associated with benign prostatic hyperplasia (AUA [McVary 2010]; Cunningham 2019).

Males: Oral: 5 mg once daily (either as a single agent or in combination with an alpha-1 adrenergic antagonist); 6 to 12 months of treatment is usually needed to improve symptoms (AUA [McVary 2010]; Cunningham 2019; McConnell 2003).

Hirsutism (alternative agent) (off-label use): Note: Typically given in addition to oral contraceptives (OCs) if inadequate response to OCs is observed after 6 months. May be considered as initial therapy for females who cannot conceive or who are using reliable contraception.

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 (Barbieri 2019; Endocrine Society [Martin 2018]).

Dosing: Geriatric

Refer to adult dosing.


Oral: May be administered with or without meals. Pregnant women and females of childbearing potential 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

The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.

>10%: Genitourinary: Impotence (5% to 19%; [placebo: 4% to 12%])

1% to 10%:

Cardiovascular: Hypotension (1%), orthostatic hypotension (9% [placebo: 8%]), peripheral edema (1%)

Endocrine & metabolic: Decreased libido (2% to 10% [placebo: 1% to 6%]), gynecomastia (1% to 2%)

Genitourinary: Breast tenderness (≤1%), decreased ejaculate volume (2% to 4%), ejaculatory disorder (<1% to 7% [placebo: 0.1% to 2%]), sexual disorder (3% [placebo: 0.9%])

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

Respiratory: Rhinitis (1%)

<1%: Hematologic & oncologic: Malignant neoplasm of the breast (men)


Cardiovascular: Hypersensitivity angiitis (Lear 1996)

Dermatologic: Acute generalized exanthematous pustulosis (T-cell mediated localized exanthematous pustulosis) (Tresch 2011), erythematous rash (erythema annulare centrifugum) (Al Hammadi 2007), urticaria (Moreno-Fernandez 2010)

Genitourinary: Male infertility (temporary) (Chiba 2010; Ricci 2012), testicular pain (Pereira 2020)

Hypersensitivity: Fixed drug eruption (Oyama 2009)

Nervous system: Depression (may persist after discontinuation) (Welk 2017), suicidal ideation (may persist after discontinuation) (Ali 2015; Welk 2017), suicidal tendencies (may persist after discontinuation) (Welk 2017)


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 United States or Canada for the prevention of prostate cancer.

Special handling:

• Females: 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. Females of childbearing potential should not touch or handle crushed or broken tablets.

Other warnings/precautions:

• Appropriate use: Other urological diseases (including prostate cancer) should be ruled out before initiating (in benign prostatic hyperplasia [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 may be required before benefit is observed (withdrawal of treatment leads to reversal of hair growth effect within 12 months).

• Prostate specific antigen 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.

Reproductive Considerations

Use is contraindicated in females of childbearing potential. Adequate contraception is recommended if used off label in the management hirsutism in females associated with polycystic ovary syndrome (ACOG 194 2018). Females of childbearing potential should not touch or handle crushed or broken tablets.

Finasteride is present in semen. Male infertility and poor seminal quality have been reported and may be reversible upon discontinuation of finasteride. Adverse events may be dose related and, less likely, associated with doses used for male pattern hair loss (Zakhem 2019).

Pregnancy Risk Factor


Pregnancy Considerations

Based on the mechanism of action and data from animal reproduction studies, in utero exposure to finasteride may lead to abnormal development of the male genital tract. Use is contraindicated during pregnancy. Pregnant females are advised to avoid contact with crushed or broken tablets.

Patient Education

What is this drug used for?

• It is used to help hair growth in male pattern baldness. It may take 3 months to see the full effect.

• It is used to treat the signs of an enlarged prostate. It may take a few months to see the full effect.

• It may be given to you for other reasons. Talk with the doctor.

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

• Sexual dysfunction

• Fatigue

• Loss of strength and energy

• Decreased sex drive

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

• Enlarged breasts

• Severe dizziness

• Passing out

• Depression

• Testicle pain

• Lump in breast

• Breast soreness or pain

• Nipple discharge

• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.

Note: This is not a comprehensive list of all side effects. Talk to your doctor if you have questions.

Consumer Information Use and Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a limited summary of general information about the medicine's uses from the patient education leaflet and is not intended to be comprehensive. This limited summary does NOT include all information available about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not intended to provide medical advice, diagnosis or treatment and does not replace information you receive from the healthcare provider. For a more detailed summary of information about the risks and benefits of using this medicine, please speak with your healthcare provider and review the entire patient education leaflet.

Further information

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