Ephedra contains ephedrine and pseudoephedrine, which are known to stimulate the central nervous system (brain and spinal cord). They activate the "fight or flight" response, resulting in constriction of blood vessels, relaxation and dilation of air passages, appetite suppression, and general stimulant effects. While these effects explain the use of ephedra as a decongestant, weight loss supplement, and anti-asthma agent, in high doses ephedra can raise blood pressure and cause adverse reactions such as stroke and heart attack. Even a single dose of an ephedra containing supplement can cause dangerous increases in blood pressure and effects on heart function.
Laboratory studies indicate that ephedra also can kill bacteria on contact, reduce inflammation, and cause contraction of the muscles of the uterus. These effects have not been studied in humans.
Ephedra is a stimulant that has caused heart attack and stroke resulting in several deaths.