Minoxidil is the generic name of an anti-hypertensive vasodilator--minoxidil dilates blood vessels. The oral medication was originally approved by the FDA for the treatment of high blood pressure in 1979. Purely by accident, physicians noticed that patients taking the drug for high blood pressure were growing lots of new hair. The rest is history.
In 1988, the FDA finally approved the drug under the trade name, Rogaine®, for topical use for hair loss, although doctors had been prescribing it off-label for that use for years previous to the approval. Now minoxidil is sold under many names worldwide.