Interesting...
I think you will have to use the table twice and union the two tables togther. In table 1 create a field called TYPE and insert the text 'Generic" and then rename your column that holds the generic name to 'MedicationName' then in version 2 of the table create a a field called TYPE and insert the text 'Trade Name' and then rename the column with the trade names to 'MedicationName'.
When you union these together you will have 1 field (TYPE) as your primary cascading param and another field (MEDICATIONNAME) for your secondary param.
There may be an easier way that I am not seeing but it is an idea anyway.