Background: The development of a safe and convenient agent that can promote hair growth in patients with androgenetic alopecia remains challenging. Objective: This study was designed to investigate the efficacy of a newly developed hair tonic containing a human umbilical cord blood mesenchymal stem cell (hUCB-MSC)-derived conditioned medium in promoting hair growth. Methods: This double-blind, placebo-controlled clinical study investigated the efficacy of a hair tonic containing an hUCB-MSC-derived conditioned medium in 30 patients with patterned hair loss. Treatment efficacy was determined using phototrichograms to evaluate the density, diameter, and hair growth rate at baseline levels and after 4, 8, and 16 weeks of treatment. Results: The hair density in the group treated with the hair tonic significantly increased from 125.2 to 134.6 hairs/㎠ (p＜0.05). In this same group, the thickness of hair also increased from 0.083 to 0.110 mm (p＜0.05). Additionally, the hair growth rate increased from 0.285 to 0.338 mm/day (p＜0.05). No severe adverse reactions were reported. Conclusion: A hair tonic containing an hUCB-MSC-derived conditioned medium could be a new effective alternative to treat patients with androgenetic alopecia. (Korean J Dermatol 2019;57(5):251∼257)