Matt Field, Psychology Professor at Liverpool University wrote us a piece about breaking habits... 

Honest (but unhelpful) answers to this question include ‘it depends’ and ‘how long is a piece of string’? Habitual behaviours, such as drinking alcohol and tobacco smoking, are difficult to ‘break’ because the constant repetition of ‘cues’ or ‘triggers’ (e.g. being in the local pub, getting home from work after a long day) and behaviour (drinking alcohol) have been associated with each other so many times, often over decades, that the mere presence of the trigger can lead to the behaviour automatically, even if we would rather do something else. Psychologists believe that it may be impossible to completely ‘unlearn’ associations that have been  established over such a long period of time.  

 However, there is good news. Rather than ‘breaking’ habits, you should think about replacing them with new ones. The trick is to identify your triggers (e.g. being with certain people, getting home from work), and make a plan for how you will deal with that situation the next time it arises. Psychologists call these plans ‘implementation intentions’. The plan should not be ‘I will not drink’ – unfortunately, that isn’t likely to work in the longer-term. However, if the plan is to actively do something different – be that turn on the TV, read a book, lace up your running shoes, phone a friend – then you are much more likely to form a new habit, that, with enough repetition, will ‘overlay’ the old habit, such that you are more likely to resist temptation.