Dry mouth, dizziness, and nausea are the most common side effects reported with Pristiq. Side effects that are less common (occurring in less than 2 percent of people) include hot flashes, nosebleeds, and yawning. Most side effects are minor and easily treated. However, contact your health care provider immediately if you experience such side effects of Pristiq as hallucinations, seizures, or panic attacks. Pristiq has been studied thoroughly in clinical trials. In these trials, one group of people was given the medication, while another group was given a placebo (a "sugar pill" with no active ingredients). This way, it is possible to see what side effects occurred, how often they appeared, and how they compared to the group who took the placebo. In these studies, the most common side effects of Pristiq (when taken at the recommended dose of 50 mg per day) included: * Nausea -- in up to 22 percent of people * Dizziness -- up to 13 percent * Dry mouth -- up to 11 percent * Diarrhea -- up to 11 percent * Increased sweating -- up to 10 percent. Other common side effects (occurring in 2 to 9 percent of people) include but are not limited to: * Constipation * Fatigue * Decreased appetite * Weight loss * Insomnia * Irritability * Abnormal dreams * Blurred vision * Ringing in the ears (tinnitus) * Decreased sex drive (libido) in men * Impotence (also known as erectile dysfunction or ED). Pristiq Side Effects to Report Some side effects with Pristiq, while occurring infrequently, are potentially serious and should be reported immediately to your health care provider. These include but are not limited to: * Suicidal thoughts or behavior (see Depression and Suicide) * Anxiety, agitation, or panic attacks * Hostility or aggressiveness * Engaging in unusual or dangerous activities * Restlessness or inability to sit still * Extreme elation or feeling of happiness that may switch back and forth with a depressed or sad mood * Other unusual changes in behavior * Signs of serotonin syndrome (a rare but dangerous problem associated with certain medications), such as: o Confusion or other mental changes o A rapid heart rate o Nausea, vomiting, or diarrhea o Hallucinations o Blood pressure changes o An irregular heart rhythm o Overactive reflexes o Fever, sweating, or shivering o Shakiness o Agitation o Seizures o Coma * Feelings of a rapidly or forcefully beating heart (known as heart palpitations) * Seizures * A high fever * High blood pressure (hypertension) * Easy bruising or bleeding * Low sodium levels in the blood (hyponatremia) * Signs of an allergic reaction, such as: o Unexplained rash o Hives o Itching o Unexplained swelling o Wheezing o Difficulty breathing or swallowing. Less Common Pristiq Side Effects Rare Pristiq side effects occurred in less than 2 percent of people taking the drug. Because these side effects are so uncommon, it is difficult to tell whether they are caused by Pristiq or something else. There is a good chance that these "side effects" could be completely unrelated to Pristiq. These less common side effects include but are not limited to: * Yawning * Hot flashes * Delayed ejaculation * Lack of orgasm * Nosebleeds * Increased LDL cholesterol ("bad" cholesterol).