Don't really understand what you mean. Only drug you really to take fast (because during combat) is (super)stim. Which don't make you invulnerable even if you take it very fast.
If its technically possible, don't see why not. As I understand it, its not so simple as us waving a magic wand and creating them - but there's little point asking me about technical stuff
I meant one superstim in a minute would heal 100HP, the second stim right afterwards would add 50 HP, giving a grisly side effect and the third one during the next 20 seconds will be your overdose, killing you, same with other drugs. You will have to wait. Or risk.