Excess levels of serotonin in the brain may cause serious or potentially life-threatening
side effects. Early signs of this problem include increased confusion and restlessness. Other possible symptoms may include weakness, fever, nausea, and anxiety. In rare cases, high levels of serotonin in the brain may cause severe complications like seizures, stroke, and even death. If venlafaxine and tramadol are used together, your doctor may want to closely monitor you for side effects.