Clenbuterol works the same way as ephedrine. However, unlike ephedrine, which is out of the body in a few hours, Clenbuterol lasts for days. So you are on it 24 hours a day. No one chooses to be on ephedrine 24 hours per day, because it interferes with sleep, and so Clenbuterol is more effective. Also, for the same effect on fat cells, Clenbuterol accelerates heart rate less, so one can use effectively a higher dose.