If I have unprotected sex with someone who has genital herpes, how likely am I to contract it if they are taking meds for it?

It depends on whether they are having a break out, but why risk it?

Agree the issue is not them taking meds, but were they currently having a signs of it. But if they were having a break out, yes a fairly good chance.

It is possible to not know they were having a break out if it was early.

If you are so concerned, you should go and have it checked out.

That is if you have already had unprotected sex.

If you haven't and want to, then don't, because you put yourself at risk.