Mounjaro is an injectable prescription medicine that is used to improve blood sugar (glucose) in adults with type 2 diabetes mellitus along with diet and exercise. Common Mounjaro side effects include: nausea, diarrhea, decreased appetite, vomiting, constipation, indigestion, and stomach (abdominal) pain. Additionally, Mounjaro presents the same serious weight loss drug side effects including: gastrointestinal side effects, a paralyzed stomach, and other weight loss drugs side effects.