Minoxidil was the first drug approved by the FDA for the treatment of androgenetic alopecia (hair loss). Before that, minoxidil had been used as vasodilator drug prescribed as oral tablet to treat high blood pressure, with side effects that included hair growth and reversal of male baldness. 

Minoxidil is a vasodilator medication known for its ability to slow or stop hair loss and promote hair regrowth. It is available over the counter for treatment of androgenic alopecia, among other baldness treatments, but measurable changes disappear within months after discontinuation of treatment.