Through a clinical trial Adriaan Kooy, MD, PhD and his team investigated whether metformin hydrochloride has sustained beneficial metabolic and (cardio) vascular effects in patients with type 2 diabetes. 390 patients treated with insulin in the outpatient clinics of 3 hospitals in a randomized, placebo-controlled trial with a follow-up period of 4.3 years were investigated. Either metformin hydrochloride 850 mg, or placebo (1-3 times daily) was added to insulin therapy. The primary end point was an aggregate of microvascular and macrovascular morbidity and mortality. The secondary end points were microvascular and macrovascular morbidity and mortality, as separate aggregate scores. In addition, effects on HbA1c, insulin requirement, lipid levels, blood pressure, body weight, and body mass index were analyzed.

Metformin was not associated with an improvement in the primary end point. It was, however, associated with an improvement in the secondary, macrovascular end point (which was partly explained by the difference in weight). Metformin, added to insulin in patients with T2DM, improved body weight, glycemic control, and insulin requirements but was not effective in cardiovascular problems.