If you do a google search you will find article after article saying that metformin never causes weight gain. But after losing from 1 to 2 pounds a month for a couple of years I started metformin. I DID NOT change my eating or exercise but as soon as I started metformin I gained weight ( 30 lbs in 3 months ) and the moment I stopped taking metformin the weight gain stopped and I have always wondered why. A couple of years after this happened I tried it again for a couple of weeks and gained 5 lbs and again when I stopped it the weight gain stopped. And yes I am a type 2 diabetic.