Drug interactions — between prescription medications, between medications and supplements, and between medications and foods — are among the most common causes of preventable harm in healthcare systems. The mechanisms are mostly pharmacological: one substance affects the liver enzymes that metabolize another, or two substances compete for the same receptor, or combined they push blood pressure or clotting beyond safe bounds. Knowing what you take, telling every prescriber your full medication list, and checking interactions before adding anything new is not paranoia but basic safety practice.
Each step builds on the last.