Explanation:
drug A is probably an antidepressant or antipsychotic drug. drug B lowers blood pressure.
Both are serious conditions, therefore, a doctor would recommend taking drug A first, drug b would interfere drug A's efficiency. dr. would recommend taking drug B at least 4 hrs. after drug A, so both drugs are effective for it's intended cause...
I hope this makes sense, it's more about which condition is more serious that you would need to treat first..
