"Only dopes use dope," goes the memorable warning about drugs. Now a Tel Aviv University researcher cautions that the same goes for cigarettes.

A study led by Prof. Mark Weiser of Tel Aviv University's Department of Psychiatry and the Sheba Medical Center at Tel Hashomer Hospital has determined that young men who smoke are likely to have lower IQs than their non-smoking peers. Tracking 18- to 21-year-old men enlisted in the Israeli army in the largest ever study of its kind, he has been able to demonstrate an important connection between the number of cigarettes young males smoke and their IQ.

The average IQ for a non-smoker was about 101, while the smokers' average was more than seven IQ points lower at about 94, the study determined. The IQs of young men who smoked more than a pack a day were lower still, at about 90. An IQ score in a healthy population of such young men, with no mental disorders, falls within the range of 84 to 116.

An addiction that doesn't discriminate

"In the health profession, we've generally thought that smokers are most likely the kind of people to have grown up in difficult neighborhoods, or who've been given less education at good schools," says Prof. Weiser, whose study was reported in a recent version of the journal Addiction. "But because our study included subjects with diverse socio-economic backgrounds, we've been able to rule out socio-economics as a major factor. The government might want to rethink how it allocates its educational resources on smoking."

Making the results more significant, the study also measured effects in twin brothers. In the case where one twin smoked, the non-smoking twin registered a higher IQ on average.

Although a lower IQ may suggest a greater risk for smoking addiction, the cross-sectional data on IQ and smoking found that most of the smokers investigated in the study had IQs within the average range nevertheless.

Obesity, drug addiction also at issue

In the study, the researchers took data from more than 20,000 men before, during and after their time in the military. All men in the study were considered in good health, since pre-screening measures for suitability in the army had already been taken. The researchers found that around 28 percent of their sample smoked one or more cigarettes a day, 3 percent considered themselves ex-smokers, and 68% said they never smoked.

Prof. Weiser says that the study illuminates a general trend in epidemiological studies. "People on the lower end of the average IQ tend to display poorer overall decision-making skills when it comes to their health," says Prof. Weiser. He adds that his finding can help address a serious concern among health counsellors at grade and high schools. Schoolchildren who have been found to have a lower IQ can be considered at risk to begin the habit, and can be targeted with special education and therapy to prevent them from starting or to break the habit after it sets in.

"People with lower IQs are not only prone to addictions such as smoking," Prof. Weiser adds. "These same people are more likely to have obesity, nutrition and narcotics issues. Our study adds to the evidence of this growing body of research, and it may help parents and health professionals help at-risk young people make better choices."