Common side effects of Cymbalta include: insomnia, hypersomnia, dizziness, weakness, drowsiness, sedation, fatigue, diarrhea, constipation, nausea, headache, and xerostomia. Other side effects include: nervousness, erectile dysfunction, psychomotor agitation, agitation, vomiting, tension, abdominal pain, decreased libido, restlessness, decreased appetite, hyperhidrosis, loss of libido, and anorexia. See below for a comprehensive list of adverse effects.