Finasteride Safety for Adults (30 to 49): What the Evidence Actually Shows

Which safety data actually apply to a man aged 30 to 49?

Nearly all of the controlled safety information in this age band comes from the hair-loss trials. Three double-blind, randomized, placebo-controlled studies of 12 months enrolled 1,879 men aged 18 to 41; the pooled safety analysis covers 945 men on finasteride 1 mg and 934 on placebo [1]. The two vertex-baldness trials that supply most of the long-term data enrolled 1,553 men aged 18 to 41, and 1,215 continued in blinded extensions for a second year [6].

That covers a man in his 30s and early 40s directly. The trials enrolled men up to age 41, so they do not directly cover men aged 42 to 49 on 1 mg. For men 45 and older with urinary symptoms, the relevant trial is PLESS, which compared finasteride 5 mg with placebo in 1,524 and 1,516 men aged 45 to 78 over four years [2].

Both strengths are prescription-only. Propecia (1 mg) is indicated for male pattern hair loss in men only and is not indicated for women [1]; Proscar (5 mg) is indicated for symptomatic benign prostatic hyperplasia [5]. HealthRX.com offers finasteride 1 mg by prescription.

How the drug works

Finasteride is a competitive, specific inhibitor of type II 5-alpha-reductase, the enzyme that converts testosterone to dihydrotestosterone; type II accounts for about two-thirds of circulating DHT, and finasteride is roughly 100-fold selective for it over type I [1]. A 1 mg tablet suppresses serum DHT by 65% within 24 hours, mean testosterone and estradiol rise by about 15% but stay within the normal range, and the drug has no affinity for the androgen receptor [1]. The enzyme complex turns over slowly, with a half-life of about 30 days for type II, so the effect on DHT outlasts the 5 to 6 hour plasma half-life in men aged 18 to 60 [1].

The recommended dose is one 1 mg tablet once daily, with or without food; daily use for three months or more is usually needed before benefit appears, continued use is needed to sustain it, and withdrawal leads to reversal within 12 months [1].

Sexual side effects at 1 mg: a small excess over placebo

In the pooled first-year data, drug-related decreased libido was reported by 1.8% versus 1.3% on placebo, erectile dysfunction by 1.3% versus 0.7%, and ejaculation disorder by 1.2% versus 0.7% [1]. Thirty-six of 945 men (3.8%) reported one or more of these versus 20 of 934 (2.1%) on placebo (p=0.04), and 1.2% versus 0.9% discontinued because of a drug-related sexual event [1].

The label adds two details. The incidence of each of these experiences fell to 0.3% or lower by the fifth year of treatment, and resolution occurred both in men who stopped the drug and in most of those who continued [1]. A self-administered sexual function questionnaire at month 12 showed statistically significant differences in favor of placebo in 3 of 4 domains — sexual interest, erections and perception of sexual problems — but no significant difference in overall satisfaction with sex life [1].

A 2019 systematic review and meta-analysis in Acta Dermato-Venereologica pooled 15 randomized, double-blind, placebo-controlled trials in 4,495 men treated for androgenetic alopecia with finasteride 1 mg or dutasteride 0.5 mg. The relative risk of sexual dysfunction with a 5-alpha reductase inhibitor was 1.57 (95% CI 1.19 to 2.08); for finasteride alone it was 1.66 (95% CI 1.20 to 2.30) [7].

How completely those events were captured is a separate question. A 2015 meta-analysis in JAMA Dermatology reviewed 34 finasteride trials for androgenetic alopecia and found that none had adequate safety reporting, 76% evaluated safety for one year or less, and funnel plots were asymmetric in a direction suggesting systematic under-detection of sexual adverse effects [8]. The same analysis found that only 31% of 5,704 finasteride-treated men in a real-world cohort would have met the entry criteria of the pivotal trials [8].

Expectation may also shape reporting. A 2007 randomized trial in the Journal of Sexual Medicine gave 120 men with BPH finasteride 5 mg described only as a proven compound for their condition, either with or without counseling that it may cause sexual side effects. Among the 107 who completed, 43.6% of counseled men reported one or more sexual side effects versus 15.3% of uncounseled men (P=0.03) [9].

Sexual side effects at 5 mg for BPH

In PLESS year one, impotence was reported in 8.1% on finasteride versus 3.7% on placebo, decreased libido in 6.4% versus 3.4%, decreased ejaculate volume in 3.7% versus 0.8%, and ejaculation disorder in 0.8% versus 0.1%; 3.7% versus 2.1% discontinued for sexual adverse reactions [2]. In years two to four there was no significant difference between groups in impotence (5.1% versus 5.1%) or decreased libido (2.6% versus 2.6%) [2]. The Proscar label states there is no evidence of increased sexual adverse experiences with longer treatment and that new reports decreased with duration [2].

Sexual effects that continue after stopping

The Propecia label's postmarketing section lists sexual dysfunction that continued after discontinuation, including erectile dysfunction, libido disorders, ejaculation disorders and orgasm disorders, and male infertility and poor seminal quality, with normalization or improvement in seminal quality reported after stopping [1]. The Proscar 5 mg label says persistent events were reported rarely in men taking 5 mg for BPH; most were older men taking other medicines, and the independent role of the drug is unknown [2].

The clearest published account is a series of standardized interviews with 71 otherwise healthy men aged 21 to 46 who reported new sexual dysfunction on finasteride for hair loss that lasted at least three months after stopping: mean finasteride use was 28 months and mean persistence 40 months [10]. An internet survey of 131 men reporting symptoms at least three months after stopping described problems across sexual, physical, cognitive and psychological domains [11]. These self-selected reports describe possible persistent symptoms but cannot establish how common they are or whether finasteride caused them. [10][11]

Depression and suicidal ideation: what the labels say

There is no boxed warning on Propecia or Proscar [1][2]. Depression and suicidal ideation sit in the Postmarketing Experience section (6.2), not in a box and not as a numbered Warnings and Precautions subsection [1]. The history is documented: the June 2021 Propecia label listed postmarketing depression, and 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 08/01/2022, changed the wording to depression, suicidal ideation and behavior [3]. The current labels describe these as voluntary reports from a population of uncertain size from which a causal relationship cannot reliably be established [1][2].

A spontaneous-report database analysis is a different kind of evidence. A 2021 case-noncase analysis of VigiBase, the World Health Organization's global database of individual case safety reports, found 356 reports of suicidality and 2,926 reports of psychological adverse events in finasteride users, with a reporting odds ratio of 1.63 (95% CI 1.47 to 1.81) for suicidality and 4.33 (4.17 to 4.49) for psychological events; the signal was stronger in men aged 45 or younger (3.47, 95% CI 2.90 to 4.15) and in men treated for alopecia (2.06, 95% CI 1.81 to 2.34) [12]. A reporting odds ratio measures how often a report mentions a drug; it does not establish that the drug caused the event.

What the cohort studies found, and who they studied

Two large cohorts looked at suicide and depression in men taking 5-alpha reductase inhibitors, and neither was made up of men aged 30 to 49 taking 1 mg for hair loss.

In Ontario, 93,197 men aged 66 or older (median age 75) who started a 5-alpha reductase inhibitor, mostly for BPH, were matched to unexposed men. Suicide risk was not increased (HR 0.88, 95% CI 0.53 to 1.45). Self-harm was higher in the first 18 months (HR 1.88, 95% CI 1.34 to 2.64) but not after, and incident depression was higher in the first 18 months (HR 1.94, 95% CI 1.73 to 2.16) and remained elevated afterward (HR 1.22, 95% CI 1.08 to 1.37). The absolute increases were 17 self-harm and 237 depression cases per 100,000 patient-years [13].

In Sweden, 2,236,876 men aged 50 to 90 were followed, of whom 70,645 started finasteride at a median age of 73. Finasteride was associated with depression (HR 1.61, 95% CI 1.48 to 1.75), constant over time, and not with completed suicide (HR 1.22, 95% CI 0.99 to 1.49) [14].

A smaller cross-sectional study compared 61 former finasteride users with persistent sexual side effects to 29 never-users with hair loss: depressive symptoms at a Beck Depression Inventory-II score of 14 or more were present in 75% (46 of 61) versus 10% (3 of 29), P<0.0001. The design is self-selected and cross-sectional and cannot prove cause [15].

PSA and prostate cancer questions for men in their 40s

Finasteride lowers PSA, so the number needs interpreting. In men aged 18 to 41 on 1 mg, mean PSA fell from 0.7 ng/mL at baseline to 0.5 ng/mL at month 12 [1]. The Proscar label reports that PSA falls by about 50% within six months, says to establish a new baseline at least six months after starting, and says to double an isolated PSA value in a man who has taken it for six months or more before comparing with normal ranges in untreated men. Percent free PSA is not changed [2]. Any confirmed increase from the lowest PSA value on treatment may signal prostate cancer and should be evaluated, even if the value is still normal for a man not taking a 5-alpha reductase inhibitor [1][2].

On high-grade disease: in the 7-year Prostate Cancer Prevention Trial in men aged 55 or older, Gleason score 8 to 10 cancer was found in 1.8% of men on 5 mg versus 1.1% on placebo, and the label states that 5-alpha reductase inhibitors may increase the risk of high-grade prostate cancer [2]. Whether the effect of reducing prostate volume or study-related factors influenced that result has not been established [2], and the Propecia label states that the clinical significance for men taking 1 mg is unknown [1]. In the same trial, prostate cancer overall was found in 18.4% versus 24.4% (a 24.8% relative reduction), while Gleason 7 to 10 tumors were more common on finasteride (6.4% versus 5.1% of men) [16]. Proscar is not approved to prevent prostate cancer [2].

Fertility, breast tissue and other labeled risks

Semen parameters were studied in healthy volunteers on 5 mg for 24 weeks: no clinically meaningful effect on sperm concentration, motility, morphology or pH, but a median 0.6 mL (22.1%) fall in ejaculate volume, reversible after stopping with an average 84 weeks to return to baseline [2]. At 1 mg, median ejaculate volume changed by -0.3 mL (-11%) versus -0.2 mL (-8%) on placebo at 48 weeks [1].

Breast tenderness and enlargement appeared in the postmarketing lists, along with male breast cancer, for which the relationship to long-term use is unknown [1]. In the controlled Propecia trials, the incidence of breast tenderness and enlargement was not different from placebo [1]. Hypersensitivity reactions (rash, itching, hives, angioedema), testicular pain and hematospermia are also listed, and hypersensitivity is a contraindication [1].

Pregnancy is the other contraindication: finasteride is contraindicated in women who are or may potentially be pregnant. The label warns that women who are or may be pregnant should not handle crushed or broken tablets because of the possible risk of abnormal external genitalia in a male fetus, and states that the coated tablets prevent contact with the active ingredient during normal handling provided they have not been broken or crushed [1].

Drug interactions

The label states that no drug interactions of clinical importance have been identified and that finasteride does not appear to affect the cytochrome P450 system. Antipyrine, digoxin, propranolol, theophylline and warfarin were tested with no clinically meaningful interactions, and finasteride was used in clinical studies alongside ACE inhibitors, HMG-CoA reductase inhibitors, benzodiazepines, beta blockers, calcium channel blockers, diuretics, NSAIDs and quinolone antibiotics without evidence of clinically significant adverse interactions [1]. Finasteride itself is metabolized mainly by CYP3A4 [1].

What is not known for this age group

Two gaps stand out. The depression and suicide cohorts describe older men (median age 75 in Ontario; 73 at treatment start in Sweden), not men in their 30s and 40s taking 1 mg for hair loss [13][14]. And safety reporting in the hair-loss trials has been judged inadequate, with most trials following men for a year or less [8].