Subjects will be monitored for craving, mood, social anxiety, sleep profile and quality of life on every visit to St George's Clinical Research Facility (quality of life will be assessed only at baseline and day 28 of e-cigarette use). The subjects will be followed up with a telephone call 6 and 12 months after the end of the e-cigarette intervention to monitor their smoking/e-cigarette use behaviour and participants craving, mood, social anxiety, sleep profile and quality of life.