Addictions like smoking, drinking, drugs, shopping, porn browsing, etc are effectively escape mechanisms that a person indulges in so as to avoid facing the core issue in his life. Addicts suffer from low self esteem or similar personal issues and thus feel a void within them. Addictions are formed because it helps the addict to temporarily fill that void with something more pleasurable.
But soon, the addiction will only help increase the feeling of void within and by that time the person has developed dependency on the addiction and he cannot live without it.
It is this void that has to be dealt with and any good Hypnotherapist does that first. Once the void is addressed the addiction can be easily cured even with simple suggestions.