My 81 year old mother-in-law has been taking valium, hydrocodone, and antivert to combat her vertigo, menieres disease, and back pain. What are the drug interactions between these medications? I know some drugs when taken together can have detrimental effects. Some increase the effects of the drugs and as valium and the opioids all affect the central nervous system. I worry the continued use will have serious effects for my mother-in-law. Her general practioner does not know how much or how often she takes these drugs as she doesn't give him accurate information. Any answer about how these drugs effect each other and how long they stay in the system would be greatly appreciated.