I need advice on how to help a young teenager with a coca-cola addiction. What can I do to help him give it up?

My 14yr old boy was a great water drinker but for the past 2yrs since starting high school has developed the taste for coke. He cannot go a day without it now and a I am worried about the negative health impact it is having on him (although not visible yet). What would be the best way to curb this addiction…any suggestions welcome!