Monday, November 29, 2010

Challenging the Received Wisdom on Tobacco Addiction


What does it take to get hooked on nicotine?

--Smokers who smoke five or fewer cigarettes per day can still become addicted to tobacco.

--Tobacco addiction can also be present in non-daily smokers.

--Nicotine withdrawal symptoms do not necessarily begin within 24 hours.

These and other controversial assertions come from Joseph R DiFranza, a physician with the Department of Family Medicine and Community Health at the University of Massachusetts Medical School. Dr. DiFranza recently authored a provocative examination of smoking truisms in an article for the online publication Harm Reduction Journal.

In an attack on what he calls the Threshold Model of Addiction, DiFranza defines the model as follows:

In brief, the threshold model maintains that until tobacco consumption is maintained above a threshold of 5-10 cigarettes per day (cpd) for a prolonged period, smokers are free of all symptoms of tobacco addiction. It holds that declining blood nicotine levels trigger withdrawal symptoms so quickly that addicted smokers must protect their nicotine levels by smoking at least 5 cpd. The threshold model states that until addiction is established with moderate daily smoking, smoking is motivated and maintained by peer pressure, pleasure seeking and the social rewards of smoking.

DiFranza breaks this prevailing paradigm into a half-dozen hypotheses, offering his opinion on the state of scientific evidence that, in his view, refutes every one of them:

--Hypothesis 1. Tobacco addiction cannot occur in nondaily smokers, or even in daily smokers who regularly consume fewer than 5 cpd.

DiFranza’s response:   “Although it is difficult to prove a negative, this hypothesis would be supported if study after study demonstrated that all surveyed subthreshold smokers (individuals who smoke < 5 cpd) have no symptoms of addiction…. Since no studies have demonstrated a complete lack of addiction symptoms in any representative population of subthreshold smokers, the peer reviewed literature soundly refutes the hypothesis that tobacco addiction requires as a prerequisite the daily consumption of 5-10 cigarettes. The threshold model and the DSM are wrong. “

--Hypothesis 2. Tobacco addiction requires prolonged daily use as a prerequisite.

Response: “Many subjects developed symptoms quite soon after the onset of intermittent tobacco use. These findings have been replicated in several longitudinal studies, in cross-sectional studies showing symptoms of addiction in nondaily smokers, and by case histories showing the same.”

Hypothesis 3. Nicotine withdrawal symptoms begin within 24 hours in all smokers.

“The standard subject in all early smoking studies was an adult who had been a heavy daily smoker for decades. Such individuals do experience nicotine withdrawal soon after their last cigarette. A problem arises when this observation is inappropriately generalized by applying it to all smokers, including children, novices and nondaily smokers.”

Hypothesis 4. Addicted smokers must maintain nicotine above a threshold blood concentration to avoid withdrawal.

“Since a person must smoke at least 5 cpd to maintain a minimum nicotine level throughout the day, another approach to testing this hypothesis would be to determine if all smokers that experience withdrawal symptoms smoke at least 5 cpd. This test has been completed over a dozen times, and always with the same result. Withdrawal symptoms have been reported in smokers of fewer than 5 cpd in every study that has examined this issue.”

Hypothesis 5. Psychosocial factors maintain smoking over the several years it may take to reach threshold levels of smoking.

“There must be thousands of studies that demonstrate that social factors such as socioeconomic status, smoking by family and friends, cigarette advertising, the availability of cigarettes, smoking depictions in movies, and attitudes and beliefs are predictive of which youth will try smoking. However, if such factors sustain tobacco use until tobacco addiction develops, they should predict which smokers will advance to addiction in prospective studies. But this has not been shown. None of more than 40 psychosocial risk factors for the onset of smoking was able to predict the progression to tobacco addiction. The author is aware of no studies that establish that peer pressure of other social factors sustain adolescent or young adult smoking over the 4 or 5 years it may take for smokers to reach threshold levels of smoking. “

Hypothesis 6. Increasing tolerance to the pleasurable effects of smoking drives the escalation in tobacco use up to the threshold of addiction.

“The author is not aware of any studies that demonstrate that smokers must smoke more cigarettes over time to obtain the same amount of pleasure (for example smoking 10 cpd to obtain the same pleasure initially obtained from smoking 1 cpd. Indeed, our data indicate that the pleasure obtained from smoking each cigarette actually increases in proportion to the degree of addiction, with pleasure ratings correlating strongly with addiction severity. While this is only one study, it directly contradicts the hypothesis that non-addicted novice smokers obtain much more pleasure from each cigarette than do addicted heavy smokers.”




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