Metformin and berberine have both been shown to decrease blood sugar. Metformin is FDA-approved to lower blood glucose in patients with type 2 diabetes. Berberine has been shown to decrease blood sugar in smaller studies and has not been evaluated by the FDA.Metformin and berberine have both been shown to decrease blood sugar. Metformin is FDA-approved to lower blood glucose in patients with type 2 diabetes. Berberine has been shown to decrease blood sugar in smaller studies and has not been evaluated by the FDA.