There's rogaine and propecia. Though you have to be wary of the side effects.
And if you stop taking them, your hair will stop growing back.

Sometimes it'll go away. If you're wearing a hat a lot, or are dying or straightening or even blow drying your hair too frequently, that can cause you problems. If you're doing any of these things that I've mentioned, stop.

That might help stop the hairloss. Also, try eating foods high in iron and protein. Those two components help build up parts of the body and are related to generation of hair.