Metformin is a good safe drug, but has limited effect on blood sugars, so it is unlikely this is the reason why your mum's glucose levels have dropped by such a lot. It does help, but not by a lot. It helps the liver and has some other good qualities. I believe it is mainly an appetite suppressant. To get her levels down, as Mo said above, she would need to reduce her carbohydrates as they all turn to sugar once in the system. Being active will help, especially if she can increase her exercise a little. One thing for sure, Metformin alone won't help a great deal. It is down to diet and exercise. I can't help feeling this sounds cruel for a lady of her age! I wish her all the best.