Smokers in clinical studies who say they've quit often haven't

This nationwide study followed five large smoking cessation clinical trials in the US that enrolled smokers at hospitalization. At 6-month follow-up, 822 participants (out of 4,206 who completed the follow-up survey) reported they had not smoked in the past 7 days and provided a usable saliva sample for verification by testing for a chemical called 'cotinine'. The liver converts nicotine in the body to cotinine and so this chemical is a very accurate measure of whether someone has smoked in the past few days. More than 40% of those 822 self-reported quitters failed the saliva test.

The misreporting rate may be even higher because, despite the offer of $50 to $100 for providing a sample 18.6% of people who had said they had quit smoking did not reply, even after multiple attempts. These participants were excluded from the study. The study also excluded anyone who said they were using another nicotine product such as smokeless tobacco, nicotine patches or e-cigarettes. Even very heavy exposure to other people smoking would not have raised cotinine levels to those found in this study.

Lead author Dr. Taneisha Scheuerman says "Our study shows that in studies where participants may feel pressure to say they have quit when they have not, it is essential to verify claims of quitting using an objective test such as cotinine to know true quit rates. For clinical researchers, another important finding is that misreporting rates were similar across intervention and control conditions, suggesting that the relative effectiveness of interventions tested was the same using self-report and cotinine levels."

Professor Robert West, Editor-in-Chief of the journal, Addiction, that published the article comments, "Other research has shown very low misreporting rates in population surveys of smoking. Hospital patients and pregnant women would be likely to feel strong pressure to have stopped smoking."