What is oral minoxidil?

Oral minoxidil contains the same active ingredient as topical minoxidil (generic Rogaine). While topical minoxidil is FDA-approved for hair loss and available over-the-counter, oral minoxidil is used "off label" and requires a prescription. Originally FDA-approved at higher doses for high blood pressure, doctors noticed that low-dose oral minoxidil could effectively treat hair loss due to its side effect of promoting hair growth.