He (Kevorkian) used sodium pentathol, potassium chloride, and pancuronium bromide. Same stuff they use for lethal injection. They have to be injected in a specific sequence to make the process pain free and humane, which is why you need the machine to do it to yourself. You will be unconscious after they inject the pentathol and the other two drugs come in to paralyze you and stop your heart from beating. If you were conscious during this process you would be in a great deal of agony when the potassium chloride was infused. Kevorkian had two different machines because after the first couple of euthanasia's, his medical license was revoked and he couldn't get his hands on the drugs, so the later machine used carbon monoxide gas to kill the patient.