Finasteride Vaccine Interaction Profile: What Clinicians and Patients Need to Know

What the labels say about interactions

The Propecia label (effective October 14, 2024) states in its Drug Interactions section: "No drug interactions of clinical importance have been identified. Finasteride does not appear to affect the cytochrome P450-linked drug-metabolizing enzyme system" [1]. The compounds tested in humans were antipyrine, digoxin, propranolol, theophylline and warfarin, with no clinically meaningful interactions found [1].

The Proscar label (effective March 18, 2026) carries the same statement [2]. It adds a second subsection listing drug classes used alongside finasteride in clinical studies without evidence of clinically significant adverse interactions: ACE inhibitors, alpha-blockers, anticonvulsants, benzodiazepines, beta blockers, calcium-channel blockers, diuretics, H2 antagonists, statins, NSAIDs and quinolone anti-infectives [2]. No vaccine is named in either list.

Does finasteride touch the immune system?

The label describes a narrow target. Finasteride is a competitive, specific inhibitor of Type II 5-alpha reductase, the enzyme that converts testosterone to dihydrotestosterone (DHT) [1]. That isozyme is found mainly in the prostate, seminal vesicles, epididymides and hair follicles, plus the liver, and accounts for about two-thirds of circulating DHT [1]. Finasteride is roughly 100-fold selective for Type II over Type I, and a 1 mg tablet suppresses serum DHT by 65% within 24 hours [1]. Mean testosterone and estradiol rise by about 15% but stay within the normal range, and the drug has no affinity for the androgen receptor [1].

Nothing in the Propecia label's pharmacology or its Warnings and Precautions section describes an effect on immune function [1].

What the labels warn about instead

The cautions in the Propecia label are pregnancy (a contraindication, including handling of crushed or broken tablets), PSA reduction, high-grade prostate cancer and sexual adverse effects [1]. Mean PSA fell from 0.7 to 0.5 ng/mL at month 12 in men aged 18 to 41 [1]. In the 7-year Prostate Cancer Prevention Trial of finasteride 5 mg, Gleason 8 to 10 cancer was found in 1.8% of men on finasteride versus 1.1% on placebo [1][2]. In three 12-month Propecia trials (945 men on drug, 934 on placebo), 3.8% versus 2.1% reported decreased libido, erectile dysfunction or ejaculation disorder (p=0.04) [1].

An FDA labeling change for Propecia was approved August 1, 2022 [5]. The current Propecia label lists depression, suicidal ideation and behavior as postmarketing reports [1]; the Proscar label lists depression and suicidal ideation [2]. Both labels note that these reports are voluntary, come from a population of uncertain size and cannot reliably establish cause [1][2]. None of this is a vaccination issue.

Where do live vaccines fit?

Neither label lists a live vaccine, or any vaccine, as a contraindication or a precaution [1][2]. The contraindications are pregnancy and hypersensitivity to any component [1][2].

The one place finasteride and a vaccine appear together

A 2025 pharmacovigilance analysis of 11,465 FDA adverse-event reports from 2004 to 2024 flagged gum disorders as a signal for finasteride and, separately, for COVID-19 vaccines, using disproportionality methods [3]. That kind of analysis detects reporting patterns in a spontaneous database; it cannot show that either product causes gum disorders, and it reports each product separately rather than an interaction between them [3].

The practical answer

The CDC adult immunization schedule sets recommendations by age and by medical condition [4]. Neither label gives a timing instruction between a finasteride dose and a vaccine. Propecia is taken as one 1 mg tablet once daily, with or without food [1]; Proscar is taken as one 5 mg tablet once daily [2].