I'm trying to find a movie I think from the 80s - I can't remember much but there's a boy I think his sister is taken by they monsters or goblins - the boy ends up making a potion/ drink in his kitchen it turns out blue or green - he drinks it so he can go to the world where his sister is --- anyone have a clue what I'm talking about?

I think you mean Labyrinth (http://www.imdb.com/title/tt0091369/)!