Headaches, dizziness, and nausea are some of the more common side effects seen with Paxil CR^® (paroxetine controlled release). Uncommon Paxil CR side effects (occurring in 2 percent to 5 percent of people) can include muscle tightness, migraines, and a rapid heart rate. In most cases, Paxil CR side effects are minor and either do not require treatment or can easily be treated. However, certain side effects are more serious and should be reported to your healthcare provider right away. A few of these more serious side effects include suicidal thoughts or behavior, hallucinations, and unusual changes in behavior.