Hello! I read your question carefully and understood your concern. A wide range of antidepressants is available nowadays. Sometimes the patient respond poorly to the use of monotherapy. In these case the right dose-effect ratio should be checked, if the patiet take it properly. If nothing wrong is found, a higher dose may be used or another antidepressant of the same group or of another group can be prescribed. If any of these thechniques aren t successful, than a combination of two antidepressants should be considered. Citalopram belongs to selective serotonin reuptake inhibitors (SSRI) and duloxetine belongs to serotonin and norepinephrine reuptake inhibitors (SNRI). These two drugs are used concomitantly, so a lower dose of each can be used with greater effect, with the least of adverse effects, the most dangerous the serotonin toxicity. I would mostly agree with your doctor, but other coombination and treatment strategies can be used further, if the tretament isn t going to help. I m would be glad to assist you with further questions. Kind regards