Improvement of insulin action is an important part of the antidiabetic effect of metformin.

Although biguanides are widely used in the treatment of non-insulin- dependent diabetic patients, the underlying mechanism for their antidiabetic effects is not fully understood. There is circumstantial evidence that their mode of action is multifactorial. It is unknown, however, to what extent the different single effects contribute to the overall antidiabetic effect. Recent studies indicate that metformin treatment improves peripheral insulin action, which might occur both at the receptor level and/or at the postreceptor site. It is now generally accepted that postreceptor defects are of major importance for the insulin resistance of type-II diabetic patients. Findings indicating that metformin might influence postreceptor sites of insulin action seem, therefore, to be more relevant than possible effects on insulin receptor binding.