My wife has been passing these for the past year and it used to be once a month or so. But is now several per day several days a month. She is on Metformin. She has also been experiencing a ton of swelling and inflammation and other symptoms that have the doctors not knowing what is going on. This is the first place I have seen a picture of what is coming out of her and other people with similar experiences. My original theory is that maybe it was a gallstone, but I just saw the link to gallstone pictures and they look different.