Medications are a particular problem. It took decades of massive use for us to even realize that some of our most common over-the-counter drugs were being used in dangerous ways (e.g. aspirin can cause Reye's syndrome in children, Tylenol with alcohol can damage the liver). On top of that, I think drug interactions are a much larger problem than most people realize and that we have little idea of what we are doing to ourselves when we take multiple medications. A recent study [1] on just prescription drugs counted 220 million unique drug combinations experienced by a subset of the US population over intervals of about 3 years. How many of those combinations have been studied for safety? I'll make a wild guess that it's probably far less than 1%. I think it prudent to minimize one's medication exposure to the bare minimum that is absolutely necessary.