My recommendation for the opening, speaking generically, is to have an initiating event. An action. As has been said above, just talking about wanting to kick an addiction is a bit cliche' if not a bit "on the nose" so to speak.
I would consider starting with introducing your characters in their current life. A day in the life of your main character/protag as an addict.
Then you should have an initiating event or action that changed the trajectory of your character/protagonist onto the path (in this case, kicking their addiction). But be aware that this too is full of cliches like "friend ODs" or "gets arrested stealing to fund the addiction", etc. but that doesn't mean you can't use that, just that you need to execute it well.
So again my recommendation is to show us the path your characters are on, introduce a triggering or initating event or action that changes that trajectory and then we're on the path of the story you want to tell.