Each year, hundreds of thousands of people in rural areas of developing countries lose their lives to organophosphorus (OP) pesticide poisoning. These toxic chemicals disrupt the body’s nervous system by blocking critical enzymes, and treating such cases often relies on antidotes like pralidoxime chloride—yet figuring out if these drugs are working has long been a clinical challenge. For decades, some doctors have turned to measuring butyrylcholinesterase (BuChE) activity in the blood to gauge treatment success. BuChE is an enzyme inhibited by OP pesticides, and its reactivation after antidote administration seems like a logical marker of progress. But new research suggests this practice might be misleading—especially for the moderately toxic “WHO…