I think his brain would get hooked on the experience of the drug. He is getting the high, after all, and that's got to do something to his brain. OTOH, it could also have some interesting side effects on his magic, since he's using a spell to ride-along on the high.
I didn't think of this as a Severus and Lucius story when I was writing it. It's definitely a Snarry in my mind -- with a Severus who is still trying to keep his balance between two worlds. He's just doing it to himself this time, instead of allowing two masters to do it to him.