Ephedrine is the principal active ingredient in the herb ephedra or ma huang.
It is similar in form to the appetite control drug phenylpropanolamine (now banned in the U.S.), also known as norephedrine, meaning ephedrine whose methyl group has been replaced by a hydrogen.
It is also similar to the controlled stimulant amphetamine, which is norephedrine with the hydroxyl group replaced by a hydrogen.
Pseudoephedrine is an isomer of ephedrine, with the hydroxyl group on the other side of the molecule.
Ephedra is used in diet products as an appetite depressant and stimulant, and in sports drinks to mask fatigue.
It is also used as a bronchial stimulator, and to relieve symtoms of the common cold.
Ephedrine enhances the release of the hormone norepinephrine in the body, and also binds to the same receptors as that hormone, causing excess calories to be converted to heat instead of being stored as fat. It also raises blood pressure. Epinephrine and norepinephrine are also known as adrenaline and noradrenaline. Ephedrine thus acts to stimulate an "adrenaline rush".
Interactions with caffeine and aspirin can increase the effects of ephedrine. Norepinephrine works in part by increasing the levels of cyclic AMP in cells. Caffeine inhibits the enzyme that breaks down cyclic AMP. Together, ephedrine makes more cyclic AMP, and caffeine prevents it from breaking down. Aspirin inhibits the receptors that turn off release of norepinephrine. So ephedrine releases norepinephrine, and aspirin prevents the release from being turned off.
Ephedrine by itself has been shown to be ineffective as a weight loss treatment. Ephedrine combined with either caffeine or aspirin was effective. The effect appears to be caused by a reduction in appetite, and preventing the metabolic rate decrease usually associated with a reduced calorie diet.
Due to its effect as a stimulant on the heart and central nervous system, ephedrine can cause heart problems, stroke, and other medical complications (including death), and there is pressure to regulate it or ban it in the U.S., as was done with its close cousins.