Glitazones (pioglitazone and rosiglitazone), are also used in combined double and triple therapy and now account for more than half of what Britain's National Health Service spends on oral drugs for the regulation of blood sugar.

An exhaustive study of the available evidence led Britain's Drug and Therapeutics Bulletin to conclude that glitazones have a place in combined treatments with either metformin or a sulphonylurea for people with type 2 diabetes who are unsuited to one or other of these older drugs.

But the Bulletin said there is "no convincing evidence" that when taken alone the glitazones produce greater health benefits than either of the other types of treatment.