What do systematic reviews say?

Metformin vs placebo

Metformin leads to higher adverse effects associated with the treatment: diarrhoea compared with placebo (high certainty).

• Metformin for women who are overweight or obese during pregnancy for improving maternal and infant outcomes 2018 · Cochrane Headline outcomes only
  RR 2.34 [1.74, 3.14]
  2 studies · 797 participants
  High