Sedatives like what she used (implied to be M-99 by the color) don't cause addictions. It's not even a painkiller so it's not in the same class as drugs like morphine or vicodin. It just puts you out. All his confused hallucinations were based on real events and his own thoughts. Sherlock was implied to be into cocaine anyway, which is a different class from painkiller/sedative drugs.
Don't think I'm trying to wank or nitpick you, I just know too much about drugs and like spouting off things I know. *shame*
Incidentally, long term side-effects of sedatives just involve drowsiness for days, but looks like he dodged that one.