The present invention is drawn to combinations of pharmaceutical agents having similar chemical and/or pharmacological properties, wherein the combinations maximize the therapeutic effect of the drug while minimizing their adverse effects. The methods and compositions of the invention are particularly useful in the treatment of obesity and related conditions which involves treating a subject with a sympathomimetic agent (e.g., phentermine or a phentermine-like drug) or bupropion in combination with an anti-epileptic agent (e.g., topiramate, zonisamide), CB1 antagonists (e.g., rimonabant), or a 5HT2C-selective serotonin receptor agonist, (e.g., lorcaserin) for the treatment of obesity and related conditions. The invention also features kits for use in the practice of these novel therapies.