In this analysis, data from both randomised controlled trials and a “real-world” cohort demonstrated that metformin use is associated with early, small reductions in haemoglobin level, resulting in increased rates of moderate anaemia in people with type 2 diabetes. The real-world, observational data, with up to 20 years of follow-up, demonstrated that, for each 1 g per day of metformin, there was a 2% higher risk of moderate anaemia per year. The authors conclude that they would not advocate avoidance or discontinuation of metformin due to anaemia risk, because the benefits of metformin are proven, the effects on anaemia are modest and the mechanisms are unknown. However, prescribers should anticipate a reduction in haemoglobin levels in the first few years after metformin initiation.
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