In these studies, the most common side effects of Pristiq (when taken at the recommended dose of 50 mg per day) included: 1  Nausea -- in up to 22 percent of people. 2  Dizziness -- up to 13 percent. 3  Dry mouth -- up to 11 percent. 4  Diarrhea -- up to 11 percent.  Increased sweating -- up to 10 percent.