When a patient swallows a tablet, they are trusting that the active pharmaceutical ingredient inside is pure enough to help and not hurt. A big part of that trust comes down to how well the impurities in the ingredient were studied and kept in check. Impurities travel with every drug substance. You will never get rid of them all, and honestly, you do not need to. The real job is knowing what they are, deciding how much is too much, and holding them inside safe limits. This guide covers how those impurities are classified, the logic behind studying and controlling them, the three areas regulators care about most right now,…