Pretty easy to understand how MJ died when you understand that these drugs he was taking suppress your urge to breath. Thus your breathing slows down and your CO2 rises to a level you completely stop breathing.
Fentanyl another very popular street drug is a strong synthetic narcotic and it also slows or suppresses your breathing. The larger the dose the faster it kills you. Without O2 we go into cardiac arrest and die. Morbid but it is what it is.
