Patients suffering from type 2 diabetes may not benefit from taking both an oral glucose lowering drug (metformin) and insulin instead of insulin alone, a study published on claims.

The researchers say the combination leads to better , less weight gain and less need for insulin. However, they also suggest that more trials are needed to provide firm evidence about the long term benefits and harms of the combination and specifically about the risks of premature death.

, the glucose lowering drug, is currently recommended by guidelines for patients with starting on insulin.

The authors of the study, from the Copenhagen Trial Unit, Steno Hospital, and the Copenhagen University Hospital, reviewed 2217 patients in total, all of whom had type 2 diabetes and were over 18 years old.

The reporting of patient important outcomes, such as total mortality and deaths from cardiovascular disase, was very sparse among the included trials.

Twenty trials reported that levels of HbA1c (a measure of average over time) were reduced with the combined use of the drugs. (BMI) and weight gain were also significantly reduced by metformin plus insulin by an average of 1.6 kg.

The authors say that, owing to the risk of severe hypoglycaemic attack increasing with the use of metformin plus insulin, there should be further research on the long term benefits and harms of the combination of the drugs.

In this week's BMJ podcast Trish Groves (BMJ's deputy editor) talks to first author Bianca Hemmingsen about how the researchers were able to draw on more data than previous analyses, and how they looked at mortality and major complications rather than surrogate outcomes like weight and . Dr Hemmingsen discusses the lack of evidence for answering whether insulin and metformin or insulin alone is best for patients, and how trials are urgently needed.

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