Metamucil works extremely well; I’ve been using it for 4yrs, since I was declared a Type 1 diabetic; now Type 2.
I’m concerned about the 2nd part of your post — Metformin being a carcinogen. Do you have anything further on it?
I chose this site when I searched Metformin.
https://www.healthline.com/health/diabetes/metformin-side-effects
I think it some side affect on H=hubby and he had to stop it. That’s when his doc took him off and suggested Metamucil
It was a contaminant, not the active ingredient itself. Many different capsule and tablet medications have been hit by this.