It depends. For the obvious case where you are 100% bald, eg a classic receding hairline, then there is no need. But if you get a transplant into a thinning are

It depends. For the obvious case where you are 100% bald, eg a classic receding hairline, then there is no need. But if you get a transplant into a thinning area where there is still active loss happening with the remaining follicles, then finasteride is an option. Or you can wait for more hair to fall out and get more hair transplanted in, which sounds dumb but is apparently relatively common.