Both phentermine and acomplia are appetite suppressants used in combination with a healthy diet and physical exercise to support weight loss. That means they both work on the chemistry of the brain to slow down the message from the stomach that more food is required. Thus, when people are starting a diet and they might find hunger pangs a distraction, both drugs help people to keep up their morale and stay with the diet. The drugs work in different ways. Phentermine works like an amphetamine and there are possible risks of addiction. Acomplia works on the cannabinoid system and regulates addictive behavior like overeating and smoking. In making a decision between the two, note that many internet sites do not sell genuine Phentermine but fakes that have no effect.