Finasteride Side Effects Permanent? What Studies Show

How Long Finasteride's Hormonal Effect Lasts

Finasteride is a competitive inhibitor of type II 5-alpha-reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT). Type II produces about two-thirds of circulating DHT [1]. A 1 mg tablet suppresses serum DHT by 65% within 24 hours [1].

The drug's mean terminal half-life is about 5 to 6 hours in men aged 18 to 60, but the enzyme complex it binds turns over slowly, with a half-life of roughly 30 days for the type II complex, so DHT suppression outlasts the drug in the blood [1]. That is a statement about hormone levels, not about how long side effects last. The label's timing statement covers hair: continued use is needed to sustain benefit, and withdrawal leads to reversal of effect within 12 months [1].

How Often Sexual Side Effects Appeared in Trials

Three controlled 12-month Propecia trials enrolled 945 men on finasteride 1 mg and 934 on placebo, aged 18 to 41 [1]. Drug-related decreased libido was reported by 1.8% vs 1.3%, erectile dysfunction by 1.3% vs 0.7%, and ejaculation disorder by 1.2% vs 0.7% [1]. Overall, 36 of 945 men (3.8%) reported one or more of these against 20 of 934 (2.1%) on placebo (p=0.04), and 1.2% vs 0.9% stopped treatment because of them [1].

Breast tenderness, breast enlargement, hypersensitivity reactions and testicular pain were reported at rates no different from placebo in those trials [1]. The label lists male breast cancer as a postmarketing report and states the relationship to long-term finasteride use is unknown [1].

A 2019 meta-analysis of 15 randomized placebo-controlled trials (4,495 men with androgenetic alopecia) found a relative risk of sexual dysfunction of 1.57 (95% CI 1.19 to 2.08) with finasteride 1 mg or dutasteride 0.5 mg. For finasteride alone the relative risk was 1.66 (1.20 to 2.30) [7].

In the four-year PLESS trial of 1,524 men on Proscar and 1,516 on placebo, year-one impotence was 8.1% vs 3.7% and decreased libido 6.4% vs 3.4%, with no significant difference between groups in years 2 to 4 [4]. PLESS enrolled men aged 45 to 78 with BPH; the Propecia trials enrolled men aged 18 to 41 with hair loss [1][4].

What the Labels Say About Effects That Continue

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' [1]. The Medication Guide puts it plainly: 'decrease in sex drive that continued after stopping the medication' and 'problems with ejaculation that continued after stopping medication' [1]. Neither Propecia nor Proscar has a boxed warning; these statements sit in the postmarketing and patient sections of the Propecia label [1][4].

The Propecia label says these reports are voluntary, come from a population of uncertain size, and cannot establish how often an effect occurs or whether finasteride caused it [1]. The Proscar label says persistent sexual events were reported rarely in men taking 5 mg for BPH; most were older and taking other medicines, and Proscar's independent role is unknown [4].

In May 2022, FDA ordered a Propecia labeling change citing suicidal ideation and behavior, additional sexual dysfunction risk, and psychoneurocognitive adverse events [8]. Supplement S-030, approved 08/01/2022, changed the psychiatric wording to 'depression, suicidal ideation and behavior' [8].

What the Persistence Studies Found

One study used standardized interviews with 71 otherwise healthy men aged 21 to 46 who reported new sexual side effects on finasteride for hair loss that lasted at least three months after stopping [9]. Mean finasteride use was 28 months and mean persistence 40 months; 94% reported low libido, 92% erectile dysfunction, 92% decreased arousal and 69% problems with orgasm [9]. The men volunteered because they had the symptoms, so the study cannot say how common persistence is or that finasteride caused it [9].

A second study by the same author compared 61 former users with persistent sexual side effects against 29 men who had hair loss and had never used finasteride. Scores of 14 or more on the Beck Depression Inventory II occurred in 75% (46 of 61) vs 10% (3 of 29), p<0.0001 [10]. That study was small, cross-sectional and self-selected, so it cannot prove cause [10].

A 2020 review in Fertility and Sterility argued that post-finasteride syndrome is a real condition in a subset of men and noted that many clinical studies assess adverse events incompletely [11]. That reporting gap has been measured: a JAMA Dermatology meta-analysis of 34 finasteride trials for hair loss found none had adequate safety reporting, 76% evaluated safety for one year or less, and funnel plots suggested sexual adverse effects were under-detected [12]. Only 31% of 5,704 men prescribed finasteride in a real-world cohort would have met the entry criteria for the pivotal trials [12].

Depression and Suicide Data

A population-based Ontario cohort compared 93,197 men aged 66 and older who started a 5-alpha reductase inhibitor, mostly for BPH, with matched men who did not [5]. Suicide risk was not increased (HR 0.88, 95% CI 0.53 to 1.45) [5]. Self-harm was higher only in the first 18 months (HR 1.88, 1.34 to 2.64) [5]. Diagnosed depression was higher in the first 18 months (HR 1.94, 1.73 to 2.16) and modestly higher afterward (HR 1.22, 1.08 to 1.37), with absolute increases of 17 self-harm and 237 depression cases per 100,000 patient-years [5].

A Swedish register study of 2,236,876 men aged 50 to 90 included 70,645 who started finasteride, with a median age at treatment of 73 [6]. Depression was more common (HR 1.61, 95% CI 1.48 to 1.75), and the hazard stayed constant over time [6]. Suicide was not associated (HR 1.22, 0.99 to 1.49) [6].

Neither cohort was made up of young men taking 1 mg for hair loss. A prospective study of 128 men with androgenetic alopecia (mean age 25.8) on finasteride 1 mg/day found that depression scores rose significantly over two months (p<0.001 on the Beck Depression Inventory, p=0.005 on the HADS depression scale) while the rise in anxiety scores was not significant (p=0.061) [13]. Scores were compared before and after treatment, without a placebo group.

Cognitive Symptoms

Two small studies measured neuroactive steroid levels in cerebrospinal fluid and plasma of former finasteride users with persistent sexual and mood symptoms and compared them with healthy controls, and found differences between the groups [14][15]. One of them had three patients and five controls [14]. The 2022 FDA labeling order cited psychoneurocognitive adverse events as new safety information [8].

Semen and Fertility

The Proscar label reports a 24-week semen study in healthy volunteers: no meaningful effect on sperm concentration, motility or morphology, but a median ejaculate volume decrease of 0.6 mL (22.1%), reversible, with an average 84 weeks to return to baseline [4]. With Propecia 1 mg, median ejaculate volume fell 0.3 mL (11%) vs 0.2 mL (8%) on placebo at 48 weeks [1]. The label lists male infertility and poor seminal quality as postmarketing reports, and notes that normalization or improvement in seminal quality has been reported after discontinuation [1].

How Common Are Lasting Effects?

The controlled trials counted side effects during treatment, and the label states these resolved in the men who stopped because of them [1]. Sexual dysfunction that continued after stopping appears in the postmarketing section, which gives no rate [1]. The two large mood studies mainly involved older men, many treated for prostate enlargement, so their findings may not apply to younger men taking finasteride 1 mg for hair loss [5][6].