This review from 2017 assessed the relationship between biotin supplementation and hair loss. With 18 studies reviewed the authors found that while biotin supplementation was effective, it was only shown to be helpful if an underlying biotin deficiency was established.
References:
Patel DP, Swink SM, Castelo-Soccio L. A Review of the Use of Biotin for Hair Loss. Skin Appendage Disord. 2017 Aug;3(3):166-169. doi: 10.1159/000462981. Epub 2017 Apr 27. PMID: 28879195; PMCID: PMC5582478.
