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Strength of Evidence Each key finding has been rated according the strength of evidence supporting it:
Multiple well-designed randomized clinical trials yielded a consistent pattern of findings. Some evidence from randomized clinical trials but the scientific support was not optimal. Limited evidence indicative of a possible effect but not sufficient to support a recommendation.
The main adverse effect of nicotine in tobacco products is addiction, which sustains tobacco use. Because most smokers are nicotine-dependent, they continue to expose themselves to toxins from tobacco. Tobacco, not nicotine, is responsible for most of the adverse health effects.
Nicotine per se is not a substantial cause of cancer. Carcinogenic nicotine-derived nitrosamines may be formed in the body under certain conditions after administration of nicotine medications. It is expected that the levels of these carcinogens will be low, but further research is needed to determine whether this level could represent a health hazard during long-term nicotine therapy. The risks during short-term therapy to aid smoking cessation are insignificant compared to the risks of smoking.
While nicotine replacement therapy during pregnancy is potentially hazardous, it is likely that nicotine therapy is less hazardous than cigarette smoking, which exposes both the mother and foetus to both nicotine and a myriad of other toxins.
Nicotine replacement products have low abuse liability compared to tobacco products, but the liability may not be equal across all medications. The abuse liability is likely to be greatest with those products that deliver nicotine rapidly. The prevalence of abuse (i.e. use for reasons other than smoking cessation) and of dependence (i.e. difficulty stopping) with currently available nicotine medications is nil (nicotine patch) or very low (<10% of users of nicotine gum, nasal spray, inhaler). Even if dependence on nicotine medications develops there is likely to be an overall health benefit if the individual is no longer smoking cigarettes.
The anti-depressants nortriptyline and moclobemide have been found in smoking cessation trials in healthy smokers to be safe in doses approved for the treatment of depression.
The benefits of bupropion to aid smoking cessation outweigh the risks of bupropion in most smokers. Data on the safety of bupropion in patients with cardiovascular disease and during pregnancy are not yet available.
Concomitant use of nicotine replacement therapy, or bupropion, and cigarette smoking is well-tolerated. Smokers may smoke fewer cigarettes during such medical therapy, which may result in reduced health hazards from their smoking, although this benefit has not been scientifically demonstrated.
“Reduced risk” cigarettes are promoted, implicitly or explicitly, to reduce the harm from smoking. Products promoted to reduce risk include low tar cigarettes and novel tobacco products that deliver nicotine with minimal combustion of tobacco. Low tar cigarettes have not been determined to substantially reduce the health hazards of smoking, while they do provide adequate nicotine to sustain nicotine addiction. Some of the novel nicotine delivery products may deliver fewer or lower levels of carcinogens and oxidant gases to smokers. On the other hand, some products deliver more carbon monoxide than regular cigarettes, and some products may expose smokers to inhalation of glass fibres. None of these products have been determined to reduce the risk of cigarette smoking or to aid smoking cessation. nicotine replacement therapy, bupropion and other medications to aid smoking cessation are most likely safer than any “reduced risk” cigarette.
Smokeless tobacco, such as snuff or chewing tobacco, has been suggested as a potential aid to harm reduction or smoking cessation. Smokeless tobacco products contain nitrosamines and other carcinogens, and are known to produce oral cancer. However, the composition of smokeless tobacco products varies from country to country. In some countries, smokeless tobacco use may be less toxic than in other countries, but this has not been adequately studied. Smokeless tobacco products are addicting. At this time smokeless tobacco is not recommended as an aid to smoking cessation. The safety and efficacy of nicotine replacement therapy and bupropion are better demonstrated.
Another approach to harm reduction is long-term pharmacotherapy with the goal to replace smoking. Both nicotine and bupropion taken over long periods are likely to be much safer than cigarette smoking. However the efficacy of long-term nicotine replacement therapy or bupropion maintenance, to reduce harm or aid cessation, has not yet been demonstrated. The long-term safety of nicotine replacement therapy remains to be tested, but is likely to be much safer than cigarette smoking. The experience with long-term use of bupropion for depression suggests that it is well tolerated.
There is little reason to believe that nicotine replacement therapy or bupropion pose a significantly greater risk to adolescents who smoke > 10 cigarettes per day compared to adults who smoke > 10 cigarettes per day. Whether nicotine replacement therapy or bupropion is efficacious in adolescents is unclear.
Multiple well-designed randomized clinical trials yielded a consistent pattern of findings.
Some evidence from randomized clinical trials but the scientific support was not optimal.
Limited evidence indicative of a possible effect but not sufficient to support a recommendation.