I’m 18 and losing hair, should I take Propecia?

You need to get good baselines, like a HAIRCHECK test (https://baldingblog.com/haircheck-test-how-it-is-done-video/) and once it is confirmed then taking finasteride is a good idea because this medication can reverse the balding process in someone of your age. Get a good doctor who can give you a Personalized Master Plan for now and the future