Metformin is a solid gda. Sure some research shows it decreasing IGF levels but AAS will counter that issue.. no problem. I've had ZERO problems growing like a weed with met.
As for OTC, I don't think any will compare. Test yourself with a glucometer and see what works for you. Glucozene actually tested pretty damn good with post postprandial numbers for me.. I was very impressed.
I wont name products because I'm a rep, but some of these Elite GDAs people always talk about.. did little to jack shiat for my blood sugar. Ala, R-Ala, NA-Rala, Anabolic Pump, and Slintensity have done positives. I can't name negatives.