Evaluation of the evidence base for effectiveness of pharmaceutical aids for smoking cessation

Where does the evidence come from?

The research was conducted by John Pierce and Elizabeth Gilpin at the University of California, San Diego, USA, and funded by the Tobacco Related Disease Research Program, California Department of Health Services.

What were the authors' objectives?

To examine trends in smoking cessation, pharmaceutical cessation aid use and success in cessation in the general California population.

What was the nature of the evidence?

The paper summarizes the results of three population-based surveys carried out in California in 1992, 1996 and 1999. 21,384 adults who were smokers in the previous year (from responses to a random-digit-dialed telephone protocol) completed interviews on tobacco-related issues. The response rate was 71.3% in 1992, 72.9% in 1996 and 68.4% in 1999. In all years there were slight differences in demographics between those selected and those who completed interviews.

What were the factors of interest?

Respondents were asked about current smoking status, whether they smoked a year previously and how much, whether they had in the past year quit intentionally for a day or longer, how long they were off cigarettes the last time they attempted cessation, and if they used a pharmaceutical aid or had other assistance for their most recent attempt in the last year. If so, they were asked how long they used the aid, whether they would recommend it to a friend and who paid for it. The analysis was stratified according to daily cigarette consumption (less than 15 cigarettes per day, or 15 or more cigarettes per day).

What were the findings?

Attempts to stop smoking among California smokers increased by 61.4% between 1992 and 1999 and nicotine replacement therapy use among quitters increased by 50.5%. 14.6% of quitters who used nicotine replacement therapy in 1999 also used an antidepressant. In 1996 and 1999 the duration of aid use was much less than recommended (median 14 days) and only about one in five users also had one-on-one or group behavioral counseling.

Use of nicotine replacement therapy increased short-term cessation success in moderate to heavy smokers in each survey year. However, a long-term cessation advantage was only observed before nicotine replacement therapy became widely available over-the-counter (August 1996). In 1999, no advantage for pharmaceutical aid users was observed in either the short or long term for the nearly 60% of California smokers classified as light smokers.

What were the authors' conclusions?

Since becoming available over the counter, nicotine replacement therapy appears no longer effective in increasing long-term successful cessation in California smokers.

How reliable are the conclusions?

The finding that in 1999 the association of nicotine replacement therapy with cessation of smoking was only short term is supported by graphical data. The finding that the short term advantage was present for moderate to heavy smokers but not for light smokers is supported by appropriate statistical tests.

However, a survey is a study design which is particularly prone to bias in the selection of participants and the results are based on responders' memories of events, which may be inaccurate. The authors themselves state that these surveys were not exclusively designed to measure cessation aid use by smokers but that sample sizes were large enough to address effectiveness of nicotine replacement therapy use. They also acknowledge that because this is not a randomized study people who choose to use a pharmaceutical aid are likely to differ from people who do not use one. Around 30% of people who were selected for interview did not respond and it is also likely that these people differ in some way from the 70% who did respond. The authors state that there were slight differences in demographics between those selected and those who completed interviews. Importantly, there are also likely to be unmeasured factors associated with successful smoking cessation which differ between the last group and the earlier groups - for example, if the 1999 group contained more smokers who find it difficult to quit, this could explain the finding. There are also issues of cost which may not be similar to the situation in the UK.

Owing to the nature of the study design, the conclusions reached by the authors cannot be relied upon. There could be several explanations for the change over time, and the therapy could still be effective for some people.

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