Thiazolidinediones, often called TZDs, are a class of type 2 diabetes medications that enhance the action of the body’s own insulin in muscle and fat, plus reduce glucose production by the liver. Taken with or without a meal. Possible side effects: water retention, weight gain, congestive heart failure, and (rarely) bone fractures. One type, rosiglitazone (Avandia), may increase heart attack risk. Medications available: pioglitazone (Actos) and rosiglitazone (Avandia).