Is there any side effects in using glucophage (metformin) to lose weight?

Diarrhea. The most common side effect to metformin is diarrhea. Other GI side effects can occur. Metformin is not a weight loss drug. It is used to treat diabetes as well as pre-diabetes, metabolic syndrome. In combination with a low carb diet and exercise it can assist with weight loss, but by itself, it does not cause significant weight loss.