This combination in particular. A speedball is simply one of the most intense and amazing feelings you can experience on this earth. The problem is, the coke stops an overdose of heroin from being dangerous to begin with, as the stimulant stops the respiratory depression from being too bad. The thing is, alcohol adds to the respiratory depression far too much, and when the coke wears off (as heroin lasts far longer), suddenly you've gone under....
The situation cannot be analyzed w/o alcohol. Combining alcohol is too much. Coke gives you sort of a 'mental buff' where it gives you your mental control back but your body still has the same amount of alcohol in it.
This allows you to do more of the alcohol, even past where you would have normally stopped and this is OK up to a point, but if the coke wears off you get re-drunk far past you could have gone. It hits you like a brick wall. Shit goes bad fast.
Coke has a much shorter duration than either alcohol or heroin. Timing is key and can get complicated. Either 2 combinations of the three are already dangerous enough.Adding the other is too much.
DEA classing is best to be ignored. The specific combination of booze and opiates has killed many due to how it depresses functions of the body like breathing. Really is a wicked one two punch.
Again, best ignore DEA classing. I have yet to figure out rhyme or reason of it.