Smokers trying to quit who took part in in a text messaging program called txt2stop more than doubled their chance of kicking the habit. Some smokers said that the text messages were like having an angel on their shoulder.

One text message reminded them that cravings usually last five minutes or less and suggested that they slowly sip a drink until their cravings passed. By texting "lapse" after they had succumbed to the lure of smoking, they would receive a message encouraging them not to give up and to continue with their attempt to quit.

Fully 10.7% of smokers who received the text messages succeeded at quitting smoking, compared to 4.9% of smokers who received only generic text messages. Quitting was defined as six months of not smoking, with no more than five cigarettes smoked during this period. This was biochemically verified.

The study started with 5,800 smokers, age 16 or older, who were willing to make an attempt to quit smoking within the next month. Half received supportive and encouraging text messages designed to help them stay tobacco-free, five messages a day for the first five weeks and then three messages a week for the next 26 weeks. The other half received text messages every 14 days thanking them for taking part in the study.

Messages covered a wide range of topics. Their goal was to provide positive feedback that would help smokers persevere in their attempt to quit. Some emphasized the benefits of quitting, while others offered specific advice on how to quit. They advised participants to get get rid of cigarettes, ashtrays and lighters and to avoid environments where they would normally smoke. Many encouraged participants to focus on their successes in quitting, not the failures. Others encouraged them to identify the challenges of quitting and make plans to overcome these challenges.

The program, from the London School of Hygiene and Tropical Medicine, was also personalized. For example, smokers who had expressed concern about weight gain while quitting would receive more messages on weight control, exercise tips and recipes. There were 186 different core text messages and 713 different personalized ones.

Participants in the study were able to receive additional messages during their most stressful moments. By texting "crave," they would receive an instant message on how to deal with cravings. One text message reminded them that cravings usually last five minutes or less and suggested that they slowly sip a drink until their cravings passed. By texting "lapse" after they had succumbed to the lure of smoking, they would receive a message encouraging them not to give up and to continue with their attempt to quit.

Smokers could also request the mobile phone number of another trial participant, so they could text each other for support. And they were allowed to use other smoking cessation support or services if they chose to. About half of all participants did so.

At the end of the study, 542 participants reported six months continuous smoking abstinence. This was biochemically verified either by testing for the tobacco metabolite cotinine in their saliva or by carbon monoxide testing of their blood.

Cotinine is short-lived within the body, with a half-life of only 20 hours, and can only be detected for a few days after the use of tobacco. So the verification was not perfect, only being able to show if a participant had smoked within the last few days. But it was better than simply taking the participants' word that they had quit smoking; about 25% of those who reported six months abstinence from smoking failed the biochemical verification. They were classed as unsuccessful at their attempt to quit.

The study offers evidence that a well-designed text messaging program can be extremely helpful to people willing to embark on the difficult task of quitting smoking.

An article on the study appears The Lancet.