Smooth muscle relaxation in the penis allows Viagra to facilitate erection. Like other stimulants it decreases appetite and increases metabolism, and shows some performance enhancement in users. Nicotine is excreted in the kidney as nornicotine, also present in tobacco, and also psychoactive. Variant structures like anabasine, anatabine, and cotinine can be isolated from tobacco. Cotinine has been used as an antidepressant.
Tobacco smoke contains a number of psychoactive compounds besides nicotine.
Gaseous toxins like carbon monoxide, small amounts of volatile species like acetone and acetaldehyde, as well as traces of other powerful alkaloids have been isolated. The addictive profile of nicotine is significantly strengthened by trace acetaldehyde. Acetaldehyde is the major toxic metabolite of ethyl alcohol , and has been posited to react with dopamine in the brain to form a narcotic agonist, TIQ . The zwitterion trigonelline is present in coffee and is formed in the body as a metabolite of nicotine. It is interesting to see how the chemistries of various plants and animals overlap, whether by accident or by the necessity to accomplish similar chemical ends.