I started out with metformin 3x 500mg, and on the box it says, metformin chlorhydrate 500mg "quantity corresponding to 390mg of metformin base". After a bad case of the metformin quick step and not being able to trust a fart, I refused to take anymore, and my doctor changed them to 2x 700mg. and on the box it says, metformin embonate 700mg "quantity corresponding to 280mg of metformin base". name of the company is Merck Serono the tablets are called Stagid 700mg. I cannot find anything out about the difference between these two. has anyone heard of them before? Oh, and everything seems to have settled down around the back end.