Avandamet^®, which is only available by prescription, is commonly used for the treatment of type 2 diabetes in adults. It is composed of rosiglitazone and metformin, two diabetes medicines that can lower and control blood sugar levels by helping to improve insulin sensitivity and decreasing sugar absorption into the body. Side effects of Avandamet may include diarrhea, upset stomach, and nausea. The combination drug comes as an oral tablet that is usually taken once or twice a day, and it should be taken at the same time each day to maintain an even level of medicine in your blood.