I don't want to quibble about it too much (since we don't really know), but physiologically contradictory drug effects don't exactly mean Cocaine, Meth, or MDMA automatically give you a +1 and Heroin, Fent, or GHB take away -1 or whatever. If a user IV's a stimulant, and then IV's a LETHAL amount of opiates, the stim won't keep them very active. At best they will be heavily sedated and drifting in and out of consciousness. This is of course not an exact science, paradoxical effects happen and adrenaline (or norepinephrine etc.) can do funny things, but based on the events we've seen on video I'd bet against actual opiate OD (but I'd put some money on heart failure mostly due to chronic polydrug abuse)