I can't tell the difference in flavor using stevia vs sugar, but I find I can focus better longer than when I imbibe sugar. If your feeling brave and want to add even more pep, try adding Carolina Reaper Pepper powder and some cinnamon to your cup.
You can also purchase the Dutch Cocoa Powder in the baking section, but it's not as nutritionally dense as the Natural Cocoa because they use a chemical to make it less acidic. It's a smoother (blander) taste and You have to add twice as much for the same nutritional benefit.
One more benefit to adding cocoa to my coffee, is I can use the same Kcup over a few times instead of once, because it still imparts the coffee goodness into the chocolate.
Update 7-24-18: Regarding the Blur's
My eyes starded getting blurry again so I decided to do some more research and I just found an interesting article that blurry eyes can be caused by metformin use. The short term Blur's that happen soon after starting the drug, may be caused because metformin lowers your blood sugar and your eyes haven't adapted yet to this new healthier existence. If You've been taking metformin for a few years though the blurry eyes could be caused by metformin blocking the absorption of nutrients like Vitamin B-12 and Co Enzym Q10. B12 helps your body maintain and protect your nerve sheathe's including the nerves to your eye's so if You start getting the "blur's" and You take metformin driver consider picking yourself up some B12 I blog about the best form of B12 here... And consider using my Trucker Diet to loose the weight so You can get off the meformin or decrease the dose.