Conflict of Interest from previous employment as a graduate student
Specific requirements for conflict of interest vary by publication. I think the situation you describe would be considered a conflict according to some but not all medical journal requirements, for those that give detailed requirements of what to report. Others give less guidance; in which case you should typically err on the side of caution and report it (all this assumes your employment was at least somewhat relevant to the area in which you are conducting research).

In any case, this is typically not a big deal. You won't have to do anything beyond reporting the conflict of interest, and it's unlikely to cause much concern. With pharma companies extensively involved in research, this sort of thing happens all the time.