Caffeine - Drink coffee to breathe easier

Caffeine is a methylxanthine stimulant found in coffee that makes morning lectures somewhat more tolerable. Methylxanthines are methylated derivatives of xanthine. Animals produce xanthine as an intermediate in the breakdown of purines (e.g. guanine or adenine, the purine bases found in DNA and RNA) to uric acid, the stuff that causes gout and is excreted in urine. Other methylxanthines include theophylline (found in tea) and theobromine (found in cocoa, and thus in chocolate).

At the biochemical level, caffeine inhibits an enzyme called phosphodiesterase (the same target of Viagra!) and blocks the action of adenosine. These actions wake you up (and produce nervousness and insomnia at high doses), get your heart pumping (increase heart rate and increase the force of heart contraction), cause vasodilatation (except in the brain), and make you have to pee (by increasing how much urine your kidney makes).

Caffeine is used to diagnose people who have a genetic predisposition to malignant hyperthermia, a condition invoked by general anaesthesia that causes your muscles to intensely contract, producing tonnes of heat such that you run an exceptionally high fever and the enzymes in your body begin to stop working and you die very quickly. Incidentally, this terrifying condition is also a side effect of ecstasy (MDMA) use and can be treated with a drug called dantrolene.

Back in the day, caffeine was used to treat asthma, since it causes bronchodilation (relaxes the smooth muscle of the airways, causing them to expand) and so can help to reverse the constriction that occurs during an asthma attack.

- Kalant H, Grant D, and Mitchell J. Principles of Medical Pharmacology 7th ed. Toronto: Saunders Canada, 2006.