OK, I have read all these posts on Metformin, and i don't believe this has to do with your weight loss! My boyfriend has taken this med. for two years, and from the beginning, he hasn't lost ANY weight! And his doctor had him taking 1000mg AM, and PM. He is diabetic. I think you changing what you're eating, the amount you eat, and walking more often is the reasons why you loose weight! And also, it is VERY, VERY unhealthy to loose 19LBS in 1 week!