Cigarettes: are they doubly addictive?

For years, nicotine has been widely acknowledged among health professionals as the agent responsible for fostering smokers' addiction to tobacco. But last week, a substance-abuse researcher described data indicating that cigarettes may actually provide an addictive double whammy. His former employer, a leading tobacco manufacturer, suppressed those findings for more than a decade.

The revelation emerged during a hearing of the House Subcommittee on Health and the Environment. By focusing on studies carried out at the Philip Morris Research Center's behavioral pharmacology lab more than a decade ago, the subcommittee hoped to learn what cigarette makers knew about their products' addictiveness -- and when.

Victor J. DeNoble, who headed the Richmond, Va., lab during its 4-year existence, described rodent studies that his group conducted. One set demonstrated that acetaldehyde -- a constituent of tobacco smoke -- triggers the same "reinforcing" behavior in animals as nicotine. Such behavior serves as a hallmark of addictive substances.

For the experiments, DeNoble and his coworkers implanted a catheter into the atrium of a rat's heart. The each rodent was placed in a cage with a lever. Pressing the lever delivered a solution into the catheter -- and thus the animal's heart.

When pressing the lever delivered only saltwater, the animals gave themselves about 8 doses a day. But when it delivered 8 micrograms of acetaldehyde per kilogram of body weight ([mu]g/kg) -- the rat equivalent of what a person could receive from smoking one cigarette -- the animals upped their daily intake to some 240 doses. When offered nicotine, the rats gave themselves 90 doses a day. However, when given the choice of a cigarette's worth of nicotine and acetaldehyde, the animals self-administered 400 doses a day.

"We were permitted to give talks [outside the company] on nicotine but never on acetaldehyde," DeNoble testified.

By late 1983, he learned that even the lab's reports on nicotine's potential addictiveness proved a threat because of litigation facing Philip Morris. In April -- without warning -- supervisors gave DeNoble a day to shut down his program. Told that the company had no work for researchers of their stature, DeNoble's team were encouraged to find work elsewhere, which they did.

But confidentiality agreements that the researchers signed forbade them from ever discussing their studies at the Richmond lab. The subcommittee got a waiver from Philip Morris so that DeNoble and a coworker could testify.

DeNoble's acetaldehyde data are new but not shocking, says Zalman Amit of Concordia University in Montreal. "Any substance that delivers low levels of acetaldehyde -- below about 30 or 40 [mu]g/kg of body weight -- should be reinforcing," his data indicate. Indeed, as the first product formed during the body's breakdown of alcohol, acetaldehyde may be responsible for the addictive properties leading to alcoholism, he says.

DeNoble's report even raises the possibility that acetaldehyde may explain the often observed link between smoking and drinking, adds Herbert D. Kleber of the Center on Addiction and Substance Abuse at Columbia University. "People who try to give up smoking find it hardest when they're drinking," he notes.

Following up on DeNoble's findings could also lead to a better understanding of nicotine's role in cigarettes, notes Jack E. Henningfield of the National Institute on Drug Abuse's Addiction Research Center in Baltimore. Certainly, he says, DeNoble's data "raise the possibility [that] acetaldehyde may be magnifying the effect of nicotine."