The most popular hair loss treatment is the FDA approved minoxidil (Rogaine). It was originally developed as a treatment for male, but it works for women as well. Though it may do little to grow more hair, it can extend the growth phase and thus can help you to keep the hair you already have, longer.
Over the counter minoxidil comes in two strengths. A 2% solution for women and 5% solution for men. Experts say women may see better results with the stronger preparation. The 2% solution is too weak for female pattern hair loss, you really need to use the 5% solution to get good results.
Generally both doses were well tolerated by the 381 women in the study without serious side effects. However, there were more side effects with the 5% solution such as more itching and irritation as well as hair growth in areas other than the scalp, such as on the forehead.
Be aware, in higher concentrations minoxidil is likely to cause scalp irritation, itching, and drynes. This is often remedied by customized minoxidil preparations available in doctors' offices.
In all cases, you should consult your doctor first.