I've used Berberine with great success. Doc wanted to put me on Metformin, but asked that we give Berberine a try first since Metformin is known to cause some digestive distress in some people.
My A1c was creeping up on the 5.8 to 6.0 range and I couldn't get it to come down no matter what I did (altered diet, etc.). Berberine and Metformin dose 1:1 the same.
Voila! A few weeks later, A1c was down to a comfortable 4.2.
So now keep an occasional eye on fasting glucose levels. When I see that creep up above 100 in the morning upon waking, I know it's time to get back on the Berberine.