Rogaine is intended as a treatment for male pattern baldness. The exact process is unclear, but according to Drugs.com, the medication might dilate blood vessels, which in turn stimulates growth. There is no scientific proof that Rogaine will provide thick hair growth for eyebrows, but it might help to rebuild eyebrows that are sparse because of over-plucking.
Wash your face and hands thoroughly, then dry with a clean towel.
Brush your eyebrows with an eyebrow brush. Pull the hair up, in the direction of hair growth. Brushing eyebrows further stimulates growth and will expose balding areas.
Dispense a small amount of Rogaine gel or foam onto a cotton swab. Run the swab over your eyebrow area. Avoid getting the medication into your eyes. Do not over-apply. You need only a thin film of the medication on your eyebrows.
Repeat the process twice a day. The rate of growth varies, but it might take some time. You should continue using the product for up to six months if you do not see results. The time of day does not matter, but once in the morning and once before bed makes application consistent.