Increased Metabolism: Ephedrine and caffeine are both powerful central nervous system (CNS) stimulants and work synergistically when taken together. The aspirin is added to prolong their effects. Stimulating the CNS raises your metabolism, causing more calories to be burned during exercise.
Energy and Alertness: Supplementing with the ECA stack may help fight mental fatigue and increase alertness. The energy-boosting effects of caffeine are well known, and ephedrine remains popular with truckers on long hauls for its fatigue-fighting effects.
Fat Metabolism: As documented by the "American Journal of Clinical Nutrition," caffeine consumption increases the oxidation of fat during exercise. Combined with the metabolism-boosting effects of ephedrine, the ECA stack does seem to be a potent fat-burning aid.
Bronchodilator: According to the Mayo Clinic, ephedrine, along with its herbal cousin ephedra, is an effective asthma medication, as is caffeine.