毒副作用是小, 但你反複說它能減肥, 與人家的說法不一樣啊

Metformin has no effect on body weight: Over the 10-year treatment period, the metformin group gained about 1 kg, the same as the dietary advice group, while the sulfonylureas group gained 3 kg, and the insulin group, 6 kg.[23][24]

http://en.wikipedia.org/wiki/Metformin#cite_note-25