The real test of a drug’s safety is to get it out to the market and into the hands of providers who ignore the labeling and contraindications. Some drugs, like cisapride, prove to be unforgiving of such indiscretions and are taken off the market. That’s the situation that gets most of the attention. Metformin may be different. It seems to be a more forgiving drug. The biguanides, of which metformin is a member, are well known to precipitate lactic acidosis, yet the condition has been difficult to attribute to metformin in the post marketing experience despite widespread contraindicated prescribing. Here’s a point- counter point on the question in a recent issue of CMAJ.
Will the labeling be relaxed for metformin? I don’t know. For now I’ll continue to observe the labeling.