They're not necessarily sugared in the sense of a regular Coke, but I'm not sure if they differentiate for the types. Monster, which has become a rather large company, sells a lot of their zero sugar / zero calorie products.

They moved to using erythritol. I drink the products and have yet to find any counter evidence erythritol isn't drastically superior to pretty much every other sweetener. It has been shown to be very safe (with studies spanning multiple decades now), very little of it is metabolized, and it doesn't cause the gastric reactions that competing products like xylitol do.

Have you done any research on the side-effects of energy drinks?

Surprisingly they're not even food as are carbonated sugary drinks aka soda/pop the FDA considers energy drinks a supplement.