Placebo-controlled studies have consistently found ephedrine in combination with caffeine to be effective in promoting moderate fat loss in the already-obese.
[4] Natural supplements that contain ephedra (aka Ma Huang) as an ephedrine substitute have been linked to cases of heart attack, stroke, and death in healthy young adults even when taken at the labeled dosage.
[10][7] This takes the form of elevated phosphodiesterase enzyme activity within the cells, as well as prostaglandin release in the synaptic junctions; both of these degrade cAMP and mitigate the thermogenic effects.
[11] Aspirin inhibits prostaglandin production outside of the cells, which, in conjunction with caffeine, greatly prolongs the thermogenic effects and increased metabolism by sustaining elevated cAMP levels.
The stack's effect on the central nervous system results in increased aerobic exercise performance, measured as time until exhaustion relative to respiratory metrics.
[13] Due to deaths linked to ephedra-containing dietary supplements and the potential use of ephedrine as a precursor in illegal methamphetamine manufacture, many countries have taken steps to regulate these products.
[1] In 2004, ephedra, a botanical source of ephedrine alkaloids, was banned by the U.S. Food and Drug Administration due to serious safety concerns, injuries, and deaths linked to ephedra-containing supplements.