I don't know if anyone has ever mentioned it, but
http://www.drugs.com is a good source if you want to check on drug interactions, drug and food interactions, and drug and supplement interactions. They also have alot of other resources that might be helpful to the members of this board.
I am very careful these days. The blood pressure medication and my other medication (all prescribed by the same doctor) had negative interactions. I was having symptoms even though I took the drugs according to the directions. I talked the doctor who didn't do much to help. I called one of the drug companies and talked to a pharmacist. It seems taking two drugs too close together was causing the problem. I reported the results to the doctor and followed the suggestions the pharmacist made. Things are better now. I ask the doctor to check for interactions whenever he wants to prescribe something and I check myself before I even put something in my body.