Not only are more people being prescribed medicine, but many are using multiple medications. This has led to an increased incidence of adverse drug reactions, as well as drug interactions. Predictable ADR's include side effects, such as the drowsiness causes by certain antihistamines, and toxic effects, such as the hair loss seen with some anti-cancer treatments. Non-predictable ADR's include hypersensitivity reactions and idiosyncratic reactions. An idiosyncratic reaction is one which occurs only in certain people.
Drug interactions have to do with the effect of a drug being altered by something else.
Vitamins, herbal supplements, and even food can even interact with medications. This is more than is spent on either heart disease or diabetes. Although most ADR's are not life-threatening, some can be severe. One thing which can be done is using a single pharmacy for prescriptions. Although many people will see more than one physician, they can usually utilize the same drug store.