Byetta (exenatide) is an injectable diabetes medicine that helps control blood sugar levels. Exenatide is used to treat type 2 (non-insulin dependent) diabetes.Side effects of Byetta include nausea, vomiting, upset stomach, diarrhea, constipation, weight loss, loss of appetite, heartburn, dizziness, or headache.yetta (exenatide) is an injectable diabetes medicine that helps control blood sugar levels. Exenatide is used to treat type 2 (non-insulin dependent) diabetes.