If you are seriously considering going out with the person, you should definitely do serious investigations beforehand. Find out how long the person has been on medication, how good they are about taking the medication and if they have had any issues since they have been on the medication.
It is also important to realize that in some circles, taking medication has become quite common-place, so it might not have the same meaning it once did. I have heard that in the Western world, approximately 1/3 or 1/4 of the population is on medication. I doubt that these statistics are true for the Yeshivish world, but they may have some truth for some segments of the Orthodox population. So there may be people taking medication today who would never have thought of taking medication at one time. I think that medication today is safer than it used to be so some people consider it like taking Tylenol.
That being said, I personally wouldn’t want to marry someone on medication. But that is a personal decision based to some extent on personal factors, and it may not be the right decision for everyone.