Finasteride and Biotin: Interaction, Lab Tests & Evidence

Bottom line: No pharmacokinetic drug-drug interaction exists between finasteride and biotin. They can be taken together without affecting each other’s absorption or mechanism. However, high-dose biotin supplements (≥5,000 mcg/day) can falsify lab tests — including PSA and thyroid tests — by interfering with immunoassay technology. Stop high-dose biotin at least 72 hours before blood tests.

The Biotin Lab Interference Problem

Many immunoassay-based laboratory tests use biotin-streptavidin chemistry. High-dose biotin supplementation interferes with this, producing falsely elevated or falsely suppressed results. Clinically important tests that can be affected:

• PSA (Prostate-Specific Antigen): Finasteride reduces PSA by approximately 50% — if your PSA is being monitored on finasteride, high-dose biotin could further falsify results
• Thyroid hormones (TSH, T4): Can appear falsely normal or abnormal
• Testosterone/DHT assays: Some hormone tests may be affected

Does Biotin Help Hair Loss?

Biotin deficiency causes hair loss. However, biotin deficiency is rare in men eating a typical diet, and supplementing biotin in men who are not deficient has not been shown in RCTs to improve hair density in AGA. Biotin supplements are heavily marketed for hair growth, but the evidence does not support efficacy in non-deficient individuals.

See: Finasteride and alcohol | Drug interactions overview | Finasteride alternatives