Finasteride (Hair Growth) (Monograph)

Drug class: Skin and Mucous Membrane Agents, Miscellaneous
- Hair Growth Stimulants
ATC class: D11AX10
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 Drugs.com on Dec 4, 2023. Written by ASHP.

Introduction

Finasteride inhibits type II 5α-reductase blocking the peripheral conversion of testosterone to 5α-dihydrotestosterone (DHT); in men with androgenetic alopecia, high-dose oral finasteride (5 mg) decreases scalp DHT concentrations to levels found in hairy scalp, reduces serum DHT, increases hair regrowth, and slows hair loss.

Uses for Finasteride (Hair Growth)

Androgenetic Alopecia

Finasteride is used orally to stimulate regrowth of hair in men with mild to moderate androgenetic alopecia (male pattern alopecia, hereditary alopecia, common male baldness). Androgenetic alopecia in men is expressed principally as baldness of the vertex (crown) of the scalp. In clinical trials, oral finasteride therapy has been 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 of finasteride on bitemporal recession have not been established. Improvement in both objective (scalp hair count) and subjective (individuals’ self-assessment of appearance) measures of hair regrowth has been demonstrated as early as 3 months following initiation of oral finasteride therapy, and objective improvement was at its maximum during the first 2 years of treatment. Continuation or maintenance of hair regrowth (based on scalp hair count) beyond 2 years of treatment has not been demonstrated; however, slowing of further progression of hair loss has been demonstrated in clinical trials with follow-up periods of up to 5 years. Current evidence indicates that oral finasteride therapy must be continued to sustain initial regrowth and subsequent slowing of hair loss; however, benefit of the drug should be reevaluated periodically. If improvement does not occur within the first year of finasteride therapy, further treatment with the drug is unlikely to provide benefit. Withdrawal of the drug leads to reversal of clinical benefit within 1 year.

Evidence of clinical benefit of finasteride is based principally on the results of 3 randomized, placebo-controlled clinical trials in men with mild to moderate androgenetic alopecia. Two of the trials were conducted in men with predominantly vertex hair loss, and the third trial involved men with hair loss in the anterior mid-scalp, with or without vertex balding. In these trials, efficacy of finasteride therapy was evaluated objectively using hair counts (e.g., number of hairs in a 1-inch diameter circle) and subjectively by investigators’ and treated individuals’ assessments of cosmetic benefit. All individuals in these clinical trials (both active drug and placebo groups) were instructed to use a specific, medicated, tar-based shampoo (Neutrogena T/Gel shampoo) to prevent seborrheic dermatitis that potentially could influence assessment of hair growth. The 2 trials in men with predominantly vertex hair loss were 1-year controlled trials with 1-year, controlled extension periods. The trials were extended for an additional 3 years in some men. As a result, some men who received finasteride during the first year of the trial continued to receive the drug for periods up to 5 years total, while others were switched to placebo for the second year and then were switched back to finasteride for years 3–5. Of the men who received placebo during the first year of the trial and participated in the extension trials, some continued to received placebo and some were switched to finasteride during the extension trials. The trial in patients with mild-to-moderate anterior mid-scalp area hair loss was a 1-year controlled trial.

In the trials in men with vertex hair loss, hair regrowth (as indicated by increases in hair counts) with finasteride therapy was demonstrated at 6 months and 1 year and was maintained with continued finasteride therapy for up to a total of 2 years, while men receiving placebo continued to have progressive hair loss. Men receiving finasteride for up to 5 years experienced a maximum improvement in hair count during the first 2 years; a gradual decline in hair count occurred in these men after the second year, although hair counts remained above baseline during up to 5 years of finasteride therapy. Men receiving placebo for up to 5 years experienced a decline in hair count that was more rapid than that observed in men receiving finasteride. At 1 year, 14% of men treated with finasteride had hair loss (defined as any decrease in hair count from baseline) compared with 58% of men receiving placebo. In men treated for up to 2 years, 17% of those receiving finasteride had hair loss compared with 72% of those receiving placebo. At 5 years, 35% of those receiving finasteride had hair loss compared with all of those receiving placebo. In men receiving finasteride for the first year who were switched to placebo for the second year, reversal of the increase in hair count was demonstrated at the end of the second year; those switched back to finasteride for years 3–5 experienced an increase in hair count to above baseline during the third year, and hair counts for years 3–5 remained above baseline. Men who were switched from placebo during the first year to finasteride during the second year had a decline in hair count during placebo therapy followed by an increase in hair count to above baseline after 1 year of treatment with finasteride; with continued finasteride therapy during years 3–5 of the trial, a gradual decline in hair count occurred.

Individuals’ subjective perceptions of hair growth, hair loss, and appearance were obtained at each clinic visit using a self-administered questionnaire. Evaluation of these self-assessments was consistent with an increase in the amount of hair, a decrease in and slowing of the rate of hair loss, and improvement in appearance in men treated with finasteride. Overall improvement according to individuals’ self-assessments was observed as early as 3 months following initiation of finasteride therapy and maintained for up to 5 years.

Investigators’ assessments of clinical efficacy were based on a 7-point scale evaluating increases or decreases in scalp hair at each clinic visit. At 1 year, investigators determined that hair growth had increased in 65% of men treated with finasteride compared with 37% of those receiving placebo, while increased hair growth at 2 years occurred in 80 or 47% of men receiving finasteride or placebo, respectively. At 5 years, investigators determined that hair growth had increased in 77% of men receiving finasteride, compared with 15% of men receiving placebo. Increased hair growth as determined by investigators occurred as early as 3 months after initiation of finasteride therapy. Based on blinded evaluation of standardized photographs of the head, an independent panel determined that increased hair growth had occurred in 48 or 66% of men treated with oral finasteride for 1 or 2 years, respectively, compared with 7 or 7% of men receiving placebo for the same periods. The panel also determined that, at 5 years, 48 or 6% of men receiving finasteride or placebo, respectively, had experienced an increase in hair growth; 42 or 19%, respectively, had experienced no change; and 10 or 75%, respectively, had experienced hair loss.

In the year-long study in patients with mild-to-moderate anterior mid-scalp area hair loss, hair counts also increased and were accompanied by patient-rated improvements in appearance.

In the trials in individuals with predominantly vertex baldness, self-assessments of finasteride therapy generally showed improvement in hair growth across racial groups (i.e., in whites, Asians, blacks, and Hispanics); black men reported dissatisfaction with hair growth in the frontal hairline and vertex but were satisfied with overall therapy.

While most men with vertex baldness had some response to finasteride in clinical trials, treatment failures occurred in 17% of men treated for up to 2 years with the drug. Finasteride does not appear to affect nonscalp hair.

Finasteride is not effective for treatment of hair loss in postmenopausal women with androgenetic alopecia and is not indicated for use in women. In a 1-year study in postmenopausal women with androgenetic alopecia, there was no improvement in hair counts, investigators’ or treated individuals’ assessments of benefit, or ratings based on standardized photographs of the head in women receiving finasteride versus those receiving placebo.

In clinical trials in men with vertex baldness, individuals receiving oral finasteride therapy reported problems in the areas of sexual interest, erections, and perception of sexual problems substantially more frequently than those receiving placebo at the end of 1 year; however, no substantial difference between finasteride and placebo regarding overall satisfaction with sex life was reported. Breast enlargement and tenderness have been reported during clinical trials in men receiving finasteride 5 mg daily for benign prostatic hyperplasia (BPH) and during postmarketing surveillance in men receiving finasteride 1 mg daily for androgenetic alopecia. Breast neoplasm has been reported during clinical trials of 4–7 years’ duration in men receiving finasteride 5 mg daily and during postmarketing surveillance in men receiving finasteride 1 mg daily; whether a causal relationship exists between long-term finasteride use and breast neoplasia in men has not been established. Men receiving the drug should be instructed to report any breast changes (e.g., lumps, pain, nipple discharge) to their clinician.

Oral finasteride therapy has been associated with small reductions (from 0.7 to 0.5 ng/mL) in serum prostate-specific antigen (PSA) in men 18–41 years of age receiving the drug at a dosage of 1 mg daily for androgenetic alopecia, and PSA reductions of approximately 50% have been demonstrated in older men receiving the drug at a dosage of 5 mg daily for BPH. Such reductions should be considered when interpreting serum PSA values in men receiving finasteride. Any confirmed increase in serum PSA concentration during finasteride therapy should be evaluated carefully.

5α-Reductase inhibitors may increase the 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 in men at least 50 years of age, 5α-reductase inhibitor therapy was associated with an overall reduction in prostate cancer occurrence, which reflected a reduction in lower-grade (Gleason score of 6 or less) tumors; however, the incidence of high-grade tumors (Gleason score of 8–10) was increased in men receiving finasteride or dutasteride. Finasteride is not labeled by the US Food and Drug Administration (FDA) for prevention of prostate cancer.

Finasteride is contraindicated in women who are or may potentially be pregnant. Since finasteride inhibits the conversion of testosterone to dihydrotestosterone, the drug could cause abnormalities in the external genitalia of a male fetus if a pregnant woman received the drug, and female patients should be apprised of the potential fetal hazard. In addition, pregnant women should not handle crushed or broken finasteride tablets because of the possibility of absorption and subsequent risk to the male fetus.

For use in the management of benign prostatic hyperplasia, see Finasteride 92:08.

Finasteride (Hair Growth) Dosage and Administration

Administration

Finasteride is administered orally; the drug may be given without regard to meals.

Dosage

Finasteride is recommended only for use in men. The manufacturer states that the drug is not indicated for use in women or children.

Patients should be instructed to read the patient information provided by the manufacturer before initiating finasteride and each time the prescription is renewed.

For treatment of androgenetic alopecia in men, the usual dosage of finasteride is 1 mg once daily. Daily administration of the drug for 3 months or longer generally is necessary before benefit is observed. Continued use is recommended to sustain benefit, which should be reevaluated periodically; reversal of clinical benefit occurs within 1 year after discontinuance of finasteride.

The elimination rate of finasteride decreases slightly with increasing age of the patient, ranging from about 5–6 hours in men 18–60 years of age to 8 hours in men older than 70 years of age. The manufacturer states that these findings are not clinically important and that a reduction in finasteride dosage in geriatric individuals is not warranted.

Dosage in Renal and Hepatic Impairment

Values for finasteride area under the plasma concentration-time curve (AUC), maximum plasma concentration, elimination half-life, and protein binding in patients with chronic renal failure (creatinine clearance: 9–55 mL/minute) were similar to those in healthy individuals, and the manufacturer recommends no dosage adjustment for finasteride in patients with renal insufficiency.

Because finasteride is extensively metabolized in the liver, mainly via cytochrome P-450 (CYP) isoenzyme 3A4, and the effect of hepatic impairment on finasteride pharmacokinetics has not been established, the drug should be used with caution in patients with liver dysfunction.

Description

Finasteride is a synthetic 4-azasteroid compound. The drug is a specific, competitive inhibitor of steroid type II 5α-reductase, an intracellular enzyme present in high concentrations in the liver, skin, and prostate gland. The conversion of testosterone to the active metabolite 5α-dihydrotestosterone (DHT) depends on the presence of this enzyme.

5α-Reductase is present as 2 distinct isoenzymes, type I and type II, in humans and certain animals. Type I 5α-reductase is found principally in the sebaceous and sweat glands of the skin, including scalp, follicular and epidermal keratinocytes, and dermal papilla cells, and also in the liver; this isoenzyme is responsible for approximately one-third of circulating DHT. The type II isoenzyme is found predominantly in the prostate, seminal vesicles, epididymides, and liver, and is detectable in the inner root sheath of hair follicles and epidermal keratinocytes; this isoenzyme is responsible for two-thirds of circulating DHT. Although testosterone is the principal circulating androgen, conversion to DHT amplifies the androgenic effect in androgen-sensitive target tissues such as the skin and scalp.

In men with androgenetic hair loss, increased amounts of DHT and 5α-reductase lead to miniaturized hair follicles and a shortened hair growth cycle; these alterations are not seen in hairy scalp portions of men with androgenetic hair loss or in patients without alopecia. Evidence that testosterone (and DHT) and steroid 5α-reductase may be involved in androgenetic hair loss comes from clinical observations in men with congenital 5α-reductase deficiency and in hypogonadal men. Androgenetic hair loss is not observed in these men, and hair loss in hypogonadal men can be induced by administration of testosterone. In men with congenital 5α-reductase deficiency (pseudohermaphroditism), the gene for type II 5α-reductase activity is defective, while the gene for type I isoenzyme activity remains unaffected. These data suggest that while the type II isoenzyme is not as prevalent in human scalp as the type I isoenzyme, the type II isoenzyme is involved in the development of androgenetic alopecia.

The exact mechanism of action of finasteride in patients with androgenetic alopecia has not been fully elucidated since the role of 5α-reductase and DHT in male-pattern baldness has not been fully elucidated. In vitro binding studies indicate that finasteride inhibits type II 5α-reductase by binding tightly to the enzyme and is 100-fold more selective for this isoenzyme than for the type I isoenzyme. Inhibition of 5α-reductase by finasteride is accompanied by reduction of finasteride to dihydrofinasteride and adduct formation with nicotinamide adenine dinucleotide phosphate (NADP⁺). This enzyme complex has a slow rate of turnover in the body (half-life of about 30 days for the type II isoenzyme complex and 14 days for the type I complex). Although in vitro studies suggest that finasteride acts principally through type II 5α-reductase, some clinicians suggest that chronic treatment with finasteride also may have some effect on the type I isoenzyme.

Inhibition of type II 5α-reductase by finasteride blocks the peripheral conversion of testosterone to DHT, resulting in substantial reductions in serum and tissue DHT concentrations. In men with androgenetic alopecia, high-dose oral finasteride (5 mg) decreases scalp DHT concentrations to levels found in hairy scalp, reduces serum DHT, increases hair regrowth, and slows hair loss. Finasteride may affect scalp hair growth through reductions in local and systemic DHT because the scalp is highly vascularized; the relative contributions of reductions in serum and scalp concentrations to the observed increase in scalp hair has not been elucidated.

Finasteride has no affinity for the androgen receptor and has no androgenic, antiandrogenic, estrogenic, antiestrogenic, or progestational effects.

Preparations

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.