If you mean toxic by poisonous, my opinion is no. Your body needs the sugar. It’s all about nutrient timing. For example, breakfast, pre and post workout is when your body can actually use sugar.
But if you mean poisonous being addictive, then I do think it would affect the body in that way. Call me captain obvious but anything in excess would cause dependence eventually and of course unwanted side effects and in this case being fat. Ever heard of “eat fruits and get fat”? It’s totally possible.
Hope I’ve helped.
In best health,