What is Sibutramin 20mg? Sibutramin 20mg is used in combination with a reduced calorie diet and exercise to help people who are overweight lose weight and maintain their weight loss. Sibutramin is in a class of medications called appetite suppressants. It works by acting on appetite control centers in the brain to decrease appetite. Sibutramin 20mg is used in the management of obesity by increasing the amount of neurotransmitters serotonin and norepinephrine.Sibutramin 20mg inhibits the re-uptake of these neurotransmitters by the nerve cells and alters the balance of neurotransmitters within the nerve cells. Unlike other diet drugs (fenfluramine, dexfenfluramine) which increase release of these neurotransmitters from the cells, the action of Sibutramin 20mg is similar to anti-depressants (fluoxetine) which inhibit reuptake of serotonin.