As others have already pointed out, take care of your addictions first and you'll likely find that you enjoy the taste of real whole foods (fruit, veggies, beans, nuts, etc.). For how appetite stimulating cannabis can be, I still get lazy and don't feel like cooking healthy meals if I'm smoking every single day. And though I can't speak from personal experience here, I imagine abusing heavy opiates is probably much, much worse for that.
Break your addictions, then start getting good quality sleep and exercise because they are essential not only for keeping up a good diet, but also for maintaining a healthy appetite.