Regaine or Rogaine is also known as minoxidil, is used as a topical medication for treating hair loss. Minoxidil is not taken as an oral medication, but as an application for your hair and scalp for the treatment of hair loss. Topical minoxidil is applied twice a day to the affected areas.
How Minoxidil works is by stimulating the blood flow to the affected area which is applied. It can potentially improve the supply of blood and nutrients to your hair follicles, thus boosting the hair density and rate of growth.
As that said, the main side effects are scalp irritation and unwanted growth of facial hair. On top of that, the less common side effects can include headaches, palpitations and flushing.