Ive had some pretty nasty side effects from a drug that weren't on the label. It really sucked. I'm still dealing with them.
Let me tell you that if you goto a doctor and say that you think that side effects are related to the drug he put you on and those side effects aren't yet on the label they will treat you like you are crazy. It was really eye openning to see how doctors can talk down to patients. The drug I was taking for example can cause tendons to snap. That was known. The doctor flat out didn't believe that incrediblely painful tendinitis could be related to taking the drug.
It really sucks. I got lucky though because a month later the FDA released a new list of side effects that for this drug that included my ones. Then I got a doctor to pay attention and help me out.
I knew the side effects were related to the drug thanks to a quick google search that showed thousands of other people had experienced the same things that I had. There were literally 100,000 posts in a forum discussing what I had experienced in the previous weeks.
I can't even imagine the complexity when combining two drugs and what havoc that could cause.