Finasteride Safety in Young Adults (18 to 29): What the Evidence Actually Shows

Is finasteride approved for men aged 18 to 29?

Propecia, the 1 mg tablet (finasteride 1 mg), was approved on December 19, 1997 for male pattern hair loss (androgenetic alopecia) in men only; efficacy in bitemporal recession has not been established, and it is not indicated for women or children [1][3]. Men aged 18 to 29 sit inside the studied range: the two pivotal one-year trials enrolled 1,553 men aged 18 to 41, and 1,215 continued into a second blinded year [2]. Hair count in a 1-inch (5.1 cm2) circle of balding vertex scalp ran 107 hairs above placebo at one year and 138 above at two years (P < 0.001), while the placebo group kept losing hair [2]. A third 12-month trial covered 326 men with mid-scalp loss [3].

Dosing is one 1 mg tablet once daily, with or without food; daily use for three months or more is usually needed before benefit appears, and stopping reverses the effect within 12 months [3].

How common are sexual side effects?

Three 12-month placebo-controlled trials enrolled 945 men on finasteride 1 mg and 934 on placebo, aged 18 to 41 [3]. Drug-related decreased libido was reported by 1.8% versus 1.3%, erectile dysfunction by 1.3% versus 0.7%, and ejaculation disorder by 1.2% versus 0.7%; 36 of 945 men (3.8%) reported one or more of these versus 20 of 934 (2.1%) on placebo (p=0.04) [3]. Discontinuation for drug-related sexual events was 1.2% versus 0.9%, and the incidence of each event fell to 0.3% or lower by year five [3].

The same trials carry a less tidy result: on a self-administered sexual function questionnaire at month 12, placebo scored better in three of four domains — sexual interest, erections and perception of sexual problems — with no significant difference in overall satisfaction with sex life [3].

Pooled data point the same direction. Lee et al. meta-analyzed 15 randomized, double-blind, placebo-controlled trials with 4,495 men treated for androgenetic alopecia with finasteride 1 mg or dutasteride 0.5 mg; finasteride carried a relative risk of sexual dysfunction of 1.66 (95% CI 1.20 to 2.30) [7]. A relative risk compares two groups; it is not an individual probability of developing a symptom.

The quality of that safety reporting has itself been questioned. Belknap et al. reviewed 34 finasteride trials in androgenetic alopecia: none had adequate safety reporting, 76% evaluated safety for a year or less, and funnel plots suggested under-detection of sexual adverse effects [8]. In a cohort of 5,704 men prescribed finasteride in ordinary practice, only 31% would have met the entry criteria of the pivotal trials [8].

Do sexual side effects continue after stopping?

The Propecia label's postmarketing section lists 'sexual dysfunction that continued after discontinuation of treatment, including erectile dysfunction, libido disorders, ejaculation disorders, and orgasm disorders', and 'male infertility and/or poor seminal quality', with normalization or improvement in seminal quality reported after stopping [3]. The label also states that these reports are voluntary, come from a population of uncertain size, and cannot be used to establish a causal relationship [4]. In the controlled trials, resolution occurred in men who discontinued because of sexual side effects and in most of those who continued [3].

Irwig and Kolukula interviewed 71 otherwise healthy men aged 21 to 46 who reported new sexual symptoms lasting at least three months after stopping finasteride; mean use was 28 months and mean persistence 40 months [9]. Self-selected interviews of this kind describe a group; they cannot measure how often persistence occurs or prove the drug caused it [9].

A records-based study came at frequency differently. Kiguradze et al. searched electronic medical records at Northwestern Medicine and found that 167 of 11,909 men exposed to finasteride or dutasteride (1.4%) met a definition of persistent erectile dysfunction — ED continuing at least 90 days after stopping, with a PDE5 inhibitor prescribed — with median persistence of 1,348 days [10]. The analysis included a subgroup of men aged 16 to 42 taking 1.25 mg/day or less [10]. The design is observational, so it cannot establish what caused a recorded diagnosis.

What about depression and suicidal ideation?

Propecia carries no boxed warning. Depression and suicidal ideation and behavior are listed in section 6.2 (Postmarketing Experience), not in a boxed warning and not as a numbered Warnings and Precautions subsection [3]. The history matters: the June 2021 label listed postmarketing 'depression' under nervous system/psychiatric events; on May 31, 2022 the FDA sent a safety labeling change order under section 505(o)(4) of the FD&C Act citing new safety information on suicidal ideation and behavior, additional sexual dysfunction and psychoneurocognitive events; supplement S-030, approved August 1, 2022, changed the wording to 'depression, suicidal ideation and behavior' [4].

A systematic review pooled crude rates of depressive symptoms of 3.33% with finasteride versus 2.54% without, with a meta-analysis odds ratio of 2.14 (95% CI 1.40 to 3.27) [11].

Irwig's 2012 study compared 61 former users with persistent sexual side effects to 29 men with hair loss who had never used finasteride: 75% (46/61) scored 14 or higher on the Beck Depression Inventory-II versus 10% (3/29), P < 0.0001 [12]. It was small, self-selected and cross-sectional, so it cannot prove cause [12].

The largest mood data come from older men treated mostly for prostate enlargement. In Ontario, 93,197 men aged 66 or older who started a 5-alpha reductase inhibitor were compared with matched unexposed men: suicide hazard ratio 0.88 (95% CI 0.53 to 1.45), self-harm 1.88 (1.34 to 2.64) in the first 18 months only, and depression 1.94 (1.73 to 2.16) in the first 18 months and 1.22 (1.08 to 1.37) afterward, with absolute increases of 17 self-harm and 237 depression cases per 100,000 patient-years [13]. A Swedish register study of 2,236,876 men aged 50 to 90, of whom 70,645 started finasteride (median age 73), found depression HR 1.61 (1.48 to 1.75) and no significant suicide association (HR 1.22, 0.99 to 1.49) [14]. Neither cohort followed young men taking 1 mg for hair loss.

Does finasteride affect fertility at 1 mg?

Overstreet et al. randomized 181 men aged 19 to 41 to finasteride 1 mg or placebo for 48 weeks, followed by a 60-week off-drug period; 79 men gave sequential semen samples. There were no significant effects on sperm concentration, total sperm per ejaculate, motility or morphology [5]. The label records a median ejaculate volume decrease of 0.3 mL (-11%) on finasteride versus 0.2 mL (-8%) on placebo at 48 weeks [3].

A 34.3% sperm-count drop comes from Amory et al., who randomized 99 healthy men to dutasteride 0.5 mg (n=33), finasteride 5 mg (n=34) or placebo (n=32) for one year. Total sperm count on finasteride fell 34.3% at 26 weeks but was not significantly different from baseline at 52 weeks (-16.2%) or at the 24-week follow-up (-6.2%) [15]. That was the 5 mg dose, five times the hair-loss dose, and it suppressed serum DHT by 73% [15].

Samplaski et al. looked at a selected group: 27 of 4,400 men attending a fertility clinic who were taking finasteride, mean dose 1.04 mg/day and mean duration 57.4 months. Sperm counts rose an average of 11.6-fold after discontinuation, and no man's count fell [16]. Separately, a study of Proscar 5 mg in healthy volunteers found a 0.6 mL median decrease in ejaculate volume after 24 weeks; this is not a result for the 1 mg hair-loss dose [17].

Would a lower dose or a topical product be safer?

Drake et al. gave 249 men with androgenetic alopecia finasteride 0.01, 0.05, 0.2, 1 or 5 mg, or placebo, for 42 days. Serum DHT fell 49.5% at 0.05 mg, 68.6% at 0.2 mg, 71.4% at 1 mg and 72.2% at 5 mg, and the authors concluded that doses as low as 0.2 mg maximally suppressed scalp and serum DHT [18]. That study measured hormones at 42 days, not side-effect rates or hair counts over months, and 0.5 mg was not among the doses tested [18].

Propecia is an oral 1 mg tablet. A topical finasteride spray has also been studied, but its trial results are specific to that formulation [3][6]. Piraccini et al. ran a 24-week phase III trial of one topical finasteride spray in 458 men: target-area hair count rose 20.2 hairs versus 6.7 on placebo (P < 0.001), similar to oral finasteride, while mean serum DHT fell 34.5% with the spray versus 55.6% with oral finasteride and maximum plasma concentrations were more than 100 times lower [6]. The incidence and type of adverse events did not differ meaningfully from placebo [6]. Lower systemic exposure in that trial belongs to that spray, not to a topical with a different concentration, vehicle or daily amount.

What else does the label flag?

PSA. In Propecia studies of men aged 18 to 41, mean serum PSA fell from 0.7 ng/mL to 0.5 ng/mL at month 12; any confirmed rise from the lowest value on treatment may signal prostate cancer and should be evaluated even if it sits within the normal range for untreated men [3].

High-grade prostate cancer. In a seven-year trial of men aged 55 and older taking finasteride 5 mg, Gleason 8 to 10 prostate cancer occurred in 1.8% versus 1.1% on placebo [3]. The labels state that 5-alpha reductase inhibitors may increase the risk of high-grade prostate cancer and that the clinical significance for 1 mg users is unknown [3][17].

Pregnancy contact. Women who are or may be pregnant must not take finasteride or handle crushed or broken tablets, because of the risk of abnormal external genitalia in a male fetus; intact coated tablets prevent contact with the active ingredient [3].

Other postmarketing reports include hypersensitivity reactions (rash, itching, hives, angioedema), testicular pain, hematospermia, breast tenderness and enlargement, and male breast cancer, whose relationship to long-term use is unknown [3].

Other medicines. The label reports no drug interactions of clinical importance and states that finasteride does not appear to affect the cytochrome P450 system; it was tested with antipyrine, digoxin, propranolol, theophylline and warfarin without meaningful interactions [3]. Anticonvulsants, benzodiazepines, beta blockers, calcium channel blockers, diuretics and NSAIDs were used alongside finasteride in clinical studies without evidence of clinically significant interactions [3].