Quote from tomjayc:

Within the last six months I quit using nicotine. I seem to have a much harder time without it. But I don't want to get hooked on that crap again. Last night I read that ADD'ers get hooked on nicotine a lot easier. 15 years was long enough for me.

Its hypothesized methylphenidate's (Ritalin) action is more like nicotine and that people with hyperactivity or combined type ADHD would respond better to methylphenidate. And non-smokers who have inattentive type ADHD would respond better to amphetamines (Adderall). Ritalin responders possible having polymorphisms in DAT1 gene and amphetamines responders having 7-repeat allele polymorphism of the DRD4 gene.