Finasteride Food & Supplement Interactions

Do you need to take finasteride with food?

Propecia is labeled for one 1 mg tablet once daily, and the label states it may be administered with or without meals [1]. Oral bioavailability is about 65%, and food does not change it [1]. The Proscar label for the 5 mg tablet gives the same with-or-without-meals instruction [3].

The timing points that are in the label: daily use for three months or more is generally necessary before benefit is observed, and withdrawal of treatment leads to reversal of effect within 12 months [1].

What the label says about drug interactions

The Propecia interaction section 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 compounds tested in people were antipyrine, digoxin, propranolol, theophylline and warfarin, and no clinically meaningful interactions were found with any of them [1].

A second section lists medicines taken alongside finasteride in clinical studies rather than in dedicated interaction studies: acetaminophen, aspirin, alpha-blockers, ACE inhibitors, anticonvulsants, benzodiazepines, beta blockers, calcium channel blockers, cardiac nitrates, diuretics, H2 antagonists, statins, NSAIDs and quinolone antibiotics, with no evidence of clinically significant adverse interactions [1].

Finasteride itself is metabolized mainly by CYP3A4 [1]. The label's interaction section does not discuss inhibitors or inducers of CYP3A4 [1].

Supplements: what the label covers

The label's interaction data are about medicines, not botanicals [1]. They neither show nor rule out an interaction with supplements such as saw palmetto, St. John's wort, zinc, selenium or green tea extract.

Two supplement-adjacent topics have published data, and neither is a finasteride interaction study: soy and biotin.

Soy and hormone levels in men

A 2010 meta-analysis examined 15 placebo-controlled treatment groups and separately assessed 32 reports covering 36 treatment groups of adult men who ate soy foods, isolated soy protein or isoflavone extracts [4]. It found no significant effect of soy protein or isoflavone intake on testosterone, sex hormone-binding globulin, free testosterone or the free androgen index, under either statistical model [4]. The outcomes measured were hormone levels, not finasteride response, DHT suppression or hair counts [4].

Biotin, lab assays and PSA

Some laboratory tests rely on streptavidin-biotin binding. High circulating biotin can produce positive interference (falsely high results) in affected competitive immunoassays and negative interference (falsely low results) in affected sandwich immunoassays, and the biotin concentration needed to do this varies by test and by manufacturer [2]. The guidance notes that biotin is eliminated relatively quickly, which allows a follow-up specimen when interference is suspected [2].

Finasteride has its own effect on one common test. In men aged 18 to 41, the Propecia label reports mean PSA falling from 0.7 ng/mL to 0.5 ng/mL at month 12, and says any confirmed increase from the lowest PSA value on treatment should be evaluated for prostate cancer even if the reading is still within the normal range for untreated men [1]. The Proscar label reports PSA falling by approximately 50% within six months of treatment and says an isolated PSA value in a man treated for six months or more should be doubled for comparison with normal ranges in untreated men [3].

Bottom line

The Propecia label lists a 1 mg tablet once daily, to be taken with or without meals, and reports no clinically meaningful interactions in the medicines tested [1]. For the finasteride 1 mg tablet, the label says food does not affect bioavailability [1].