In 1953, Anthony Eden suffered an injury to his bile duct while undergoing surgery to remove gallstones. To deal with the chronic pain this caused, Eden was prescribed Drinamyl, a combination of amphetamine and barbiturate. Drinamyl has been known to impair judgement, cause paranoia and even make the person taking it to lose contact with reality. It is suspected that Eden's poor decision-making during the Suez Crisis was in large part caused by the side effects of Drinamyl.
With that in mind, what would happen if Eden's surgery went smoothly, and he never develops a need for Drinamyl? How would that affect his premiership?