Minoxidil (brand name Rogaine) is an FDA-approved hair loss treatment applied to the scalp twice a day to slow or stop the progression of male pattern baldness and thinning hair. Minoxidil is thought to help increase circulation in the scalp, which can help improve nutrients and ingredient delivery to the hair follicle, but its mechanism of action is not entirely clear. Here’s more on what you need to know about minoxidil, its primary uses, and what side effects to be aware of before taking the drug.