Although amphetamine was thoroughly tested by leading scientists for its effects in boosting or maintaining physical and mental performance in fatigued subjects, the results never provided solid grounds for approving the drug's use, and, in any case, came too late to be decisive. The grounds on which amphetamine was actually adopted by both British and American militaries had less to do with the science of fatigue than with the drug's mood-altering effects, as judged by military men. It increased confidence and aggression, and elevated “morale.”