From Lying in the Gutters:
Hellblazer readers will be familiar with the end of "Dangerous Habits" when, after forcing the demons of hell to cure his cancer rather than tear Hell apart fighting over his soul, John Constantine lights up a cigarette.
In the movie, however, he spurns his cigarette after his cure and goes for some chewing gum instead. See? He's learnt his lesson.
*whimpers*
J