Finasteride and Opioids (Oxycodone, Hydrocodone, Tramadol): Drug Interaction Guide

Is there a known interaction between finasteride and oxycodone, hydrocodone or tramadol?

Finasteride's prescribing information (Propecia, 1 mg) states that no drug interactions of clinical importance have been identified, and that finasteride does not appear to affect the cytochrome P450-linked drug-metabolizing enzyme system [1]. The Proscar label for the 5 mg tablet carries the same language [3]. Both labels also record that finasteride was used during clinical studies with analgesics, benzodiazepines, anticonvulsants, beta blockers, diuretics and other common medicines without evidence of clinically significant adverse interactions [1][3].

The labels name analgesics as a category rather than oxycodone, hydrocodone or tramadol individually, and they do not report direct interaction tests with those opioids [1][3].

What finasteride's label says about enzymes

Finasteride is metabolized mainly in the liver by CYP3A4, and its metabolites carry no more than 20% of its activity [1]. The label's interaction section says finasteride does not appear to affect the cytochrome P450-linked drug-metabolizing enzyme system. That statement rests on testing with antipyrine, digoxin, propranolol, theophylline and warfarin, none of which showed a clinically meaningful interaction [1]. The interaction section does not discuss CYP3A4 inhibitors or inducers [1].

The opioid warnings that matter more than finasteride

FDA required boxed warnings on prescription opioid analgesics, opioid cough products and benzodiazepines about combined use, covering nearly 400 products, after an extensive review of the scientific evidence. The risks it names are extreme sleepiness, slowed or difficult breathing, coma and death [2]. The warning names benzodiazepines and other CNS depressants, including alcohol [2].

The measured overdose data concern benzodiazepines. Among 315,428 privately insured US adults aged 18 to 64 who filled an opioid prescription, concurrent benzodiazepine use carried an adjusted odds ratio of 2.14 (95% CI 2.05 to 2.24) for an emergency room visit or hospital admission for opioid overdose [4]. Among US veterans receiving opioids, a current benzodiazepine prescription carried an adjusted hazard ratio for overdose death of 3.86 (95% CI 3.49 to 4.26) [5]. Both studies were observational.

Does finasteride cause drowsiness of its own?

In the three 12-month Propecia trials (945 men on finasteride 1 mg and 934 on placebo), the drug-related adverse reactions reported by 1% or more were decreased libido (1.8% vs 1.3%), erectile dysfunction (1.3% vs 0.7%) and ejaculation disorder (1.2% vs 0.7%) [1]. Drowsiness does not appear in that table.

In the MTOPS study of 3,047 men with benign prostatic hyperplasia (768 on finasteride 5 mg, 737 on placebo), somnolence was reported by 1.7% of men taking finasteride alone and 1.5% taking placebo [3]. Doxazosin alone was 3.7% and the finasteride-doxazosin combination 3.1% [3].

Tramadol specifically

Tramadol's own label carries warnings about seizures and serotonin syndrome, and it is contraindicated with MAO inhibitors. Those warnings concern tramadol and the other medicines it is combined with, not finasteride.

Bottom line

For oxycodone, hydrocodone and tramadol, finasteride's label identifies no clinically important interactions and no effect on the CYP450 system [1]. Somnolence rates in MTOPS were similar, though not identical: 1.7% with finasteride alone versus 1.5% with placebo [3].

The risk that FDA highlights for opioids is the boxed warning about alcohol and other CNS depressants, and the sedation and slowed breathing those combinations can cause [2].