A Cochrane review included 42 studies with a total of over 31 000 smokers. The most common setting for delivery of advice was primary care. Pooled data from 17 trials of brief advice versus no advice (or usual care) revealed a small but significant increase in the odds of quitting (RR 1.66, 95% CI 1.42 to 1.94). Amongst 11 trials where the intervention was judged to be more intensive the estimated effect was higher (RR 1.84, 95% CI 1.60 to 2.13) but there was no statistical difference between the intensive and minimal subgroups. Direct comparison of intensive versus minimal advice showed a small advantage of intensive advice (RR 1.37, 95% CI 1.20 to 1.56; 15 trials, n=9775), in high risk populations this effect of intensive advice was stronger (RR 1.65, 95% CI 1.35 to 2.03; 5 trials, n=3773). Direct comparison also suggested a small benefit of follow-up visits in 12 months follow-up: With-in trial comparison with follow-up vs. single visit (RR 1.52, 95% CI 1.08 to 2.14; 5 trials, n=1254) and subgroup of interventions including multiple visits ( RR 2.22, 95% CI 1.84 to 2.68; 6 trials, n=4511). In one study, no significant differences in death rates at 20 years follow-up was.
Another Cochrane review included 47 studies with a total of over 18 000 participants.There was a small but statistically significant benefit from more intensive support (RR 1.16, 95% CI 1.09 to 1.24, 38 trials, n=15 506) for abstinence at longest follow-up (6 to 24 months). All but 4 of the included studies provided 4 or more sessions of support. Most trials used nicotine replacement therapy. In subgroup analyses, studies that provided at least 4 sessions of personal contact for the intervention and no personal contact for the control had slightly larger effects (RR 1.25, 95% CI 1.08 to 1.45; 6 trials, n=3762), as did studies where all intervention counselling was via telephone (RR 1.28, 95% CI 1.17 to 1.41; 6 trials, n=5311). No trials were judged at high risk of bias on any domain.