Are you talking about thick as in LOTS of hair, or thick as in the hair shafts are thick? There's no product to thin hair - and actually thick hair is a sign of good health, so be happy! The best way to manage thick hair is to get your hair cut with layers.
Go to a salon to get it thinned out. My hair is VERY thick also, and I get it thinned out. It takes 30 minutes just to blow dry my hair! Getting it thinned out, and using Dove shampoo n lots of conditioner works for me. Hope it helps you too!