The PDR states, “No drug interactions of clinical importance have been identified.” Compounds that have been tested include antipyrine, digoxin, propranolol, theophylline, and warfarin and no clinically meaningful interactions were found.
Also, finasteride (1 g or more), was used in studies with “acetaminophen, acetylsalicylic acid, α-blockers, analgesics, angiotensin-converting enzyme (ACE) inhibitors, anticonvulsants, benzodiazepines, beta blockers, calcium-channel blockers, cardiac nitrates, diuretics, H2 antagonists, HMG-CoA reductase inhibitors, prostaglandin synthetase inhibitors (also referred to as NSAIDs), and quinolone anti-infectives without evidence of clinically significant adverse interactions.”
This lack of effect on other medications and inability of other medications to affect a drug (finasteride) is exceedingly uncommon. Still, interactions that have yet to be identified are possible. Therefore, if any should occur report them to the FDA at 1–800–FDA–1088 or https://www.fda.gov/Safety/MedWatch/default.htm.