The present invention provides a pharmaceutical composition comprising a selective serotonin reuptake inhibitor (SSRI) and a norepinephrine reuptake inhibitor (NRI), particularly, fluoxetine and reboxetine, for treating obesity. Surprisingly, the inventor of the present invention discovered that use of especially low doses of the active compounds, particularly, at most 6 mg/day of reboxetine and at most 20 mg/day of fluoxetine, wherein the reboxetinerfluoxetine ratio is from about 1:4 to about 1:6, induces an effective weight loss in obese patients. Advantageously, the combinations of the present invention include very low doses of the active ingredients, thereby decreasing possible drug-drug interactions and adverse drug reaction.