I think you are confusing with Parkinsons, and there is a co-relation with dopamine receptors, and it's proven. Also, this being a Crohn's post, smoking also ha

I think you are confusing with Parkinsons, and there is a co-relation with dopamine receptors, and it's proven. Also, this being a Crohn's post, smoking also has benefits in curtailing Inflammatory Bowel Disease, but not Crohn's edit: more specifically smoking decreases the incidence of ulceraive colitis (an IBS)