Finasteride and Alcohol Interaction Profile: What You Need to Know

What the finasteride labels say about interactions

The Propecia label's drug interactions section opens with a flat statement: no drug interactions of clinical importance have been identified, and finasteride does not appear to affect the cytochrome P450-linked drug-metabolizing enzyme system [1]. It names the compounds tested in people (antipyrine, digoxin, propranolol, theophylline and warfarin), with no clinically meaningful interactions found [1]. A second part lists medicines used alongside finasteride in clinical studies (acetaminophen, aspirin, alpha-blockers, ACE inhibitors, anticonvulsants, benzodiazepines, beta blockers, calcium channel blockers, cardiac nitrates, diuretics, H2 antagonists, statins, NSAIDs and quinolones) without evidence of clinically significant adverse interactions [1]. Proscar's label carries the same two sections [5]. Alcohol appears in neither.

That silence has limits. Finasteride is extensively metabolized in the liver, mainly by CYP3A4, and the label's interaction section does not discuss CYP3A4 inhibitors or inducers [1]. Alcohol's absence from the labels means it is not part of the listed interaction information, not that a formal study ruled an effect out.

How finasteride and alcohol are each processed

Finasteride is a competitive inhibitor of type II 5-alpha-reductase, the enzyme that converts testosterone to dihydrotestosterone; a 1 mg tablet suppresses serum DHT by 65% within 24 hours [1]. The Propecia label says the 1 mg tablet is taken once daily with or without meals [1]. Finasteride peaks 1 to 2 hours after a dose, with a mean terminal half-life of about 5 to 6 hours in men 18 to 60 and 8 hours in men over 70 [1]. Most alcohol is oxidized in the liver [6].

Sexual side effects: what the finasteride trials show

In the three 12-month controlled trials of Propecia in men aged 18 to 41, 945 men took finasteride and 934 took placebo. 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%. Overall, 3.8% of treated men reported one or more of these against 2.1% on placebo (p=0.04) [1]. Each individual rate fell to 0.3% or lower by year five [1]. A meta-analysis of 15 randomized placebo-controlled trials covering 4,495 men with androgenetic alopecia put the relative risk of sexual dysfunction at 1.57 (95% CI 1.19 to 2.08) for 5-alpha reductase inhibitors and 1.66 (1.20 to 2.30) for finasteride alone [2].

At 5 mg, the PLESS trial followed 1,524 men on finasteride and 1,516 on placebo for four years. In year one, impotence was reported by 8.1% vs 3.7% and decreased libido by 6.4% vs 3.4%. In years two to four the rates were the same in both groups (5.1% vs 5.1% for impotence) [5].

In a separate double-blind crossover trial of 13 men, a low dose of alcohol (0.5 g/kg) raised plasma testosterone from 13.5 to 16.0 nmol/L and lowered androstenedione. The effect was not seen with 4-methylpyrazole pretreatment, which inhibited ethanol elimination by 37% [3]. That trial did not involve finasteride.

Mood and depression

The current labels list depression, suicidal ideation and behavior under postmarketing reports, and state that these reports are voluntary, come from a population of uncertain size, and cannot reliably establish a causal relationship [7]. Neither the Propecia nor the Proscar label has a boxed warning for psychiatric effects [1][5].

Two large cohorts have looked at this. In Ontario, 93,197 men aged 66 or older starting a 5-alpha reductase inhibitor, mostly for BPH, were compared with matched unexposed men. The depression hazard ratio was 1.94 (95% CI 1.73 to 2.16) in the first 18 months and 1.22 (1.08 to 1.37) afterward, with no increase in suicide (HR 0.88, 0.53 to 1.45) [8]. In Sweden, 70,645 finasteride starters among 2,236,876 men aged 50 to 90 (median age at treatment 73) had a depression hazard ratio of 1.61 (1.48 to 1.75); the suicide hazard ratio of 1.22 (0.99 to 1.49) was not statistically significant [9]. Both studies describe older men treated mostly for prostate symptoms, not men in their twenties taking 1 mg for hair loss.

The one analysis that looked at drinking and finasteride together

The Prostate Cancer Prevention Trial gave 18,882 men aged 55 or older either finasteride 5 mg or placebo for seven years [11]. A separate analysis of that trial examined alcohol, using 2,129 men who had prostate cancer detected during the trial and 8,791 men whose end-of-study biopsy was negative [4].

Heavy drinking (50 g of alcohol a day or more, or 4 or more drinks a day on 5 or more days a week) was associated with a higher risk of high-grade prostate cancer in both treatment arms combined (relative risk 2.01, 95% CI 1.33 to 3.05, and 2.17, 1.42 to 3.30) [4]. Within the finasteride arm, drinking 50 g a day or more was associated with a higher risk of low-grade cancer (RR 1.89, 1.39 to 2.56). The authors attributed that to finasteride cutting low-grade cancer risk by 43% in men who drank less than 50 g a day and having no effect in men who drank 50 g or more (interaction P=0.03) [4].

This analysis examined finasteride 5 mg and prostate cancer outcomes in older men. It does not answer whether alcohol changes finasteride's effects on hair loss, urinary symptoms, sexual function or mood.