Re: "the medicine I've just taken" and "the taken medicine", in some cases this can be clarified by the right choice of verb form, i.e. if your wallet was stolen you'd want to use passive form:
盗まれた財布
You would use 盗んだ財布 if you were talking about the thief on the other hand (if someone was caught by the police and had stolen goods on him, for example).