I watched this moved when I was in kindergarten and it had a boy in it that drank a blue drink and he turned in to a friendly monster, he dumped the drink in his moms plant

Not really complete matches, but maybe Fuzz Bucket (http://www.imdb.com/title/tt0286639/) or My Pet Monster (http://www.imdb.com/title/tt0400673/)

Your awsome thanks it has been driving me nuts for 18 years now it was my pet monster