I had been taking metformin for many years prior to being diagnosed with bladder cancer. In 2013 I began to have frequent and urgent urination that progressively worsened. Several months later I began to pass blood in my urine, at which time, I realized I had a serious problem. I made an appointment with a Urologist for a cystoscopy, and discovered that I had 5 cancerous tumors in the upper portion of my bladder. I went through 6 weeks of BCG treatments which were very successful. However, several months later, after another followup cystocopy, 2 more tumors had developed in middle potion of bladder. Again, I went through another round of BCG that got rid of those 2. In the latter part of 2015 after another followup cystocopy, 1 very aggressive tumor had developed in the neck of bladder that had metastacized in to the prostate. July of 2016 I underwent surgery to have bladder and prostate removed. I'm convinced that all this was the result of my taking metformin for so many years. My urologist had informed me that smoking, working with chemicals and artificial sweetners were the main causes of bladder cancer, which I never did any of those.