They say there are MAOIs in tobacco that increase nicotine uptake, but I'm not entirely convinced that that's the sole culprit either. I could chew some tobacco right now, or smoke a pipe or cigar, I could even inhale it, and I wouldn't have a problem. If I were to smoke a single cigarette I'd be smoking a pack a day within a week and who knows how many months or years it would take me to rectify that. Whatever it is I suspect it's done deliberately in processing.