The most common side effects of Vyvanse in ADHD include: anxiety, decreased appetite, diarrhea, dizziness, dry mouth, irritability, loss of appetite, nausea, trouble sleeping, upper stomach pain, vomiting, weight loss. The most common side effects of Vyvanse in adults with moderate to severe B.E.D. include: dry mouth, trouble sleeping, decreased appetite, increased heart rate, constipation, feeling jittery, anxiety.