Minoxidil is a vasodilator and originally was exclusively used as an oral drug (Loniten) to treat high blood pressure. It was, however, discovered to have the interesting side effect of hair growth and reversing baldness, and in the 1980s, Upjohn Corporation produced a topical solution that contained 2% minoxidil to be used to treat baldness and hair loss, under the brand name Rogaine in the United States, and Regaine outside the United States. Treatments usually include a 5% concentration solutions that are designed for men, while the 2% concentration solutions are designed for women. It is unknown how the drug stimulates hair growth.

Minoxidil is a "potassium channel agonist." It contains the chemical structure of Nitric oxide (NO), a blood vessel dilator, and may be a nitric oxide agonist. This may explain Minoxidil's ability to stimulate hair growth and treat hair loss. Since Minoxidil is a nitric oxide related compound it was suspected to act via activation of Guanylate cyclase, an enzyme involved in vasodilation, however there are no reports of cGMP or PKG activation to date.