What drug did Elvis Presley overdose on?

Elvis Presley had several drugs in his system at the time of his death , while his death still remains a mystery as the actual cause of death , he was prescribed Codeine which was something he was allergic to. He was very sick the last few years of his life , and took a lot of medications.
While in the Army, Elvis' superior officers supplied him with uppers (amphetamines) to enable him to stay awake to complete maneuvers. In the Army he
became addicted to the amphetamines, which proved to be his downfall.
A specific drug that he took was Cardiac Arrhythmia.
Since the drugs given to Elvis were all by prescription, he considered himself safe
and did not realize he was addicted until it was too late.