Tens of millions of people take creatine every day. They bought it for their muscles. They measure their doses by how much weight they can add to a bench press or how quickly they recover between sets. Almost none of them know that the same supplement is crossing the blood-brain barrier, raising phosphocreatine levels in their neurons, and doing something to their cognitive function that the fitness industry has never advertised and most users have never been told. A comprehensive review publish...