as i said in another thread asking the same, if you are taking medication it might be good to mention that, and that you need to be able to get to your medication when you need it, but they don't need to know what the medication is for. as long as you can perform your job according to reasonable expectations, it's a need-to-know basis.

if you get a job and you feel as though it is necessary to tell your manager at some point, wait until after your probationary period has passed (usually 30 to 90 days) so that they can't fire you without having proper cause.