system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does smoking a cigarette make me have to poop?
gpt
Cigarettes contain nicotine which in addition to being the main addictive ingredient is a potent parasympathetic agonist. Stimulation of the parasympathetic nervous system results in an increase in motility and relaxation (decreasing tone) of the gastrointestinal tract thus speeding up the processing of food in the gut and intestines. This buildup of feces in the colon increases pressure thus making it easier to relax the voluntary sphincters that cause defecation. This does not occur if smoking non-nicotine products (ie. Marijuana) since there is no nicotine present.