Hemp milk is made of simply the seeds of the hemp plant and won't have a psychoactive effect, but it's hella good for you. I bet it would pwn in Grape Nuts.
I'm making hempseed flour crepes for a big party this weekend, and this gives me the idea to use hemp milk in the batter instead of real milk, and make them... VEGAN! That would be awesome for some of the guests, who I know are vegetarians.