Diabetes drug metformin is at least as effective a treatment for normal and overweight type 2 diabetics as it is for obese patients, according to Australian researchers.

While metformin is a first-line therapy for obese diabetics, the researchers note in the journal Diabetes Care there has been little information about how effective the drug is for diabetics who are not obese.

So the researchers from Royal Prince Alfred Hospital in Sydney compared long-term outcomes of metformin therapy in 644 type 2 diabetics who were normal weight, overweight or obese.

They found metformin provided comparable long-term control of blood sugar levels in obese and non-obese patients, and was equally effective in both groups at preventing diabetic complications.

Moreover, patients who were not obese were able to maintain their glucose levels for a longer period without requiring additional drugs than obese diabetics.

"Metformin is at least as efficacious in the nonobese as it is in the obese," the authors concluded. "This study provides evidence-based data to support metformin use in nonobese individuals who have type 2 diabetes."