Most smokers know smoking is harmful to their health but find it hard to stop, largely because of addiction to nicotine and the habit of using cigarettes for many years. Medical nicotine (such as nicotine patch, the most widely used quit smoking product) doubles the chances of successfully quitting but doesn't deal with smoking habits. This study tests a new device, the e-cigarette, to see if it is better than nicotine patch at helping smokers quit. Participants will be randomly allocated to one of three groups: e-cigarettes with 16mg nicotine cartridges, nicotine patches, or e-cigarettes with 0 mg nicotine cartridges, used for 12 weeks. We will phone participants at one, three and six months after quit day to compare quitting, acceptability, use and side effects. Even if only modestly effective at helping smokers quit, e-cigarettes have potential for a positive health impact because of their popularity among smokers.