As I understand it, Metformin does not directly lower insulin. Better blood sugar control is effected by Metformin’s action of decreasing the amount of glucose produced by the liver, and by making our skeletal muscles more responsive to the existing insulin, i.e. improving insulin sensitivity. It does make sense to me that in the long run, lower blood sugar levels will mean less insulin production for most people, but I question how much, if any. Is our body lowering insulin production in response to the average lower blood sugar level, or is it sitting there, happy with the lower blood sugar level, and in effect saying, “Okay, blood sugar is better, I’m going to keep doing what I’d doing” - secreting the same amount of insulin?
I looked at about ten websites, and what’s common is saying that “unlike many drugs for blood sugar, Metformin does not increase insulin levels, but rather increases insulin sensitivity.” I didn’t see anything saying that “Metformin lowers insulin levels.”
This study was restricted to obese nondiabetic women with Polycystic Ovary Syndrome, and the findings were that Metformin does not significantly reduce hyperinsulinemia.
Weight loss does generally lead to lower insulin levels, and Metformin is known to suppress the appetites of many people, again an indirect effect. I’m thinking that if one isn’t losing weight, then the action of Metformin to reduce insulin levels may be slight and/or take a long time.