Metformin was originally developed (50 odd years ago) as an appetite suppressant and only afterwards was it discovered to be helpful to diabetics.
I've been taking it for about 5 years and at first I had rapid weight loss - about one and half stone in 7 weeks or so. The weight continued to come off until I'd lost about two stone. Although my appetite eventually returned to 'normal', the weight stayed off and have only recently put a few pounds (5?) back on.
Good luck,
Russ