Modified exendins and exendin agonists having an exendin or exendin agonist linked to one or more molecular weight increasing compounds, for example, polyamino acids, polyethylene glycol polymers, and related formulations and dosages and methods of administration thereof are provided. These modified exendins and exendin agonists, compositions comprising the modified exendin or the agonist thereof are useful in treating diabetes and conditions that would be benefited by lowering plasma glucose or delaying and/or slowing gastric emptying or inhibiting food intake.