Where are you flying into? For instance, in the UK juice is a Class C drug which is the lowest form. That means that as long as you have a personal supply, they haven't got an issue with it. In theory they could confiscate it and give you a verbal warning, but they don't as long as its in checked luggage. Only necessary medicine is allowed on board as hand-luggage. (no jokes please Bro about how you NEED your 2000mg Test on board a flight!!)
You can travel freely between borders. the only one that can be a pain is the ferry from France to England. The French are always on the look out for Pot-Heads trying to sneak in some dope from Amsterdam and if your in bad luck, some pot-head will end up having the whole bus searched because the dogs are onto something. But are they looking for gear - No! I have taken my personal supplies to several places like Spain, Ireland, Hungary, and Germany and not once did it raise an eyebrow.