Since 1993, minoxidil has been the most successful topical treatment for hair loss in both men and women, yet its exact mechanism of action remains unknown.
A 2004 review of minoxidil’s possible mechanisms of action (A.G. Messenger & J. Rundegren, 2004) suggests that the best evidence supports the idea that minoxidil causes hair follicles in the later phases of their resting phase (telogen) to shift prematurely into an active growth phase (anagen) sooner than they otherwise would; this causes rapid increase in hair growth. They also found good evidence that minoxidil works to thicken the hair by increasing hair diameter.
While minoxidil’s effects on other critical factors known to affect hair growth — such as cell proliferation, collagen synthesis, vascular endothelial growth factor and prostaglandin synthesis — remain uncertain, more recent research has found evidence that it may also suppress the androgen-androgen receptor responsible for androgenetic alopecia (Cheng-Lung Hsu, Jai-Shin Liu,An-Chi Lin, Chih-Hsun Yang, Wen-Hung Chung, & Wen-Guey Wu, 2014).
Understanding minoxidil’s exact mechanism of action remains today an important line of research both for the development of better hair loss treatments and for a better understanding of the biology of hair growth.