The aim of this study is to compare the cardiovascular disease event rate in smokers undertaking pharmacologically unaided smoking cessation attempts (the non-exposed group) with the event rate in smokers attempting smoking cessation assisted by pharmacological interventions - by nicotine replacement therapy (as any, or a combination, of: nasal spray, transdermal patches, inhaler or gum and tablets) or other pharmacological smoking cessation aids (e.g. bupropion [Zyban®] and varenicline [Champix®]) - in a representative UK primary care population.

Preliminary study data have indicated a possible increased cardiovascular disease risk in patients exposed to nicotine replacement therapy compared with controls (i.e. non-nicotine replacement therapy exposed patients) of a magnitude that could not reasonably be accounted for by differences in the cardiovascular risk profile of the two patient groups. Further in-depth studies in this area are warranted.

This retrospective study will compare the cardiovascular disease event risk in a group of smokers undertaking pharmacologically unaided smoking cessation attempts with the event rate in a group of smokers attempting smoking cessation assisted by pharmacological interventions (any of nicotine replacement therapy, bupropion or varenicline) in a representative UK primary care population.

There are three main types of pharmacological interventions currently available for smoking cessation, each of which has demonstrated efficacy when used in conjunction with behavioural support: nicotine replacement therapy, bupropion, and varenicline. Other medications, especially nortryptiline and clonidine, are considered to be effective adjunct therapy in smoking cessation, but they remain second-line options at this time.

Nicotine replacement therapy has been available since the 1980s and bupropion since 2000. Either approach to cessation doubles the chance of achieving abstinence when compared with unsupported quit attempts. After being granted its European licence in 2006, varenicline joined the pharmacological smoking cessation armamentarium. It is the first drug developed specifically for the treatment of tobacco dependence that contains no nicotine, and it triples smokers' chances of quitting compared with unsupported quit attempts.

As the fore-runner, nicotine replacement therapy is the longest-standing of the existing pharmacological smoking cessation interventions currently available. It aims to alleviate nicotine withdrawal symptoms by substituting the nicotine attained through tobacco smoking via alternative means (e.g. nasal sprays, inhalers, gum and tablets, transdermal patches). The various nicotine replacement therapy products available have differing durations of action and allow patients to tailor their nicotine intake according to their particular needs.For example, patches can be used to substitute for background nicotine and gums or tablets can be used to help satisfy urges.

Inclusion Criteria:

• The analysis will include an exposure group comprising smokers with no recorded smoking cessation attempts using pharmacological aids in the prior year, whose first recorded smoking cessation intervention was a cessation attempt assisted by either nicotine replacement therapy (using any of, or a combination of products) or another pharmacological smoking cessation intervention (e.g. bupropion, varenicline) at the index date.

Patients must also meet the following inclusion criteria:

• Aged: 18-75 years.
• Have at least one year of up-to-standard baseline data as defined by Clinical Practice Research Datalink (prior to the index smoking cessation attempt) and at least one year of up-to-standard outcome data (following the index smoking cessation attempt) or up-to-standard data up to the time of death if death occurred within the outcome period.

Exclusion Criteria:

Patients will be excluded from the analysis if they:

• Have had exposure to any nicotine replacement therapy or other pharmacological smoking cessation interventions in the baseline period (year prior to the index smoking cessation attempt), and/or
• Switched between types of smoking cessation interventions (i.e. nicotine replacement therapy to other pharmacological smoking cessation interventions or vice versa) during the outcome period(s). Switching between different nicotine replacement therapy products, or use of multiple nicotine replacement therapy products, will be permissible and analysis may involve a comparison of outcomes relative to nicotine exposure over the various outcome periods.

EXPOSED PATIENTS: include smokers with no recorded smoking cessation attempts using pharmacological aids in the prior year, whose index smoking cessation attempt was assisted by one of the following pharmacological interventions:

(i) nicotine replacement therapy as any, or a combination, of transdermal patches, nasal spray, gum and tablets, inhaler.

(ii) Other (e.g. bupropion, varenicline).

NON-EXPOSED PATIENTS: include smokers with no recorded smoking cessation attempts using pharmacological aids in the prior year, whose index smoking cessation attempt involved receipt of smoking cessation advice that resulted in a quit attempt unaided by pharmacological therapies.