Rexulti (Brexpiprazole) serious side effects. Tell your doctor right away if you have any serious side effects, including: trouble swallowing, fainting, interrupted breathing during sleep. Brexpiprazole may rarely cause a condition known as tardive dyskinesia. In some cases, this condition may be permanent. Tell your doctor right away if you develop any unusual/uncontrolled movements (especially of the face, lips, mouth, tongue, arms, or legs).