OTC NRT versus OTC placebo studies The OTC NRT versus OTC placebo trials were all randomised, parallel groups studies in which subjects received free product. The first study by Schneider et al29 was the only placebo controlled OTC study of nicotine gum. The study was published in 1983, 14 years before the next study and had a much smaller sample size (n = 36) than other OTC studies. In addition "laboratory changes" resulted in a notably uneven distribution of subjects to nicotine and placebo groups (13 v 23). Finally, when contacted, the author believed that this study did not represent an OTC setting because of the amount of contact (N Schneider, personal communication, 20 September 2001). For these reasons, we decided not to include the Schneider et al study29 in the meta-analysis.

In the 1990s, four randomised, double blind trials with large sample sizes (n = 278–802) tested active versus placebo patch (table 1). The Davidson et al trial28 was similar to the other studies except it was conducted in four shopping malls. The Hays et al study31 was conducted at five study sites including private offices or storefronts. The study first randomised subjects into one of two trials: (1) a randomised, two group OTC NRT versus OTC placebo trial in which subjects received free patches; or (2) a one group, open label trial in which subjects had to pay for patches. We did not use the open label trial in the meta-analysis because it did not have a control group.