Lighting up a cigarette may dull you to the effects of that last drink, says new research being published in the August issue of Alcoholism: Clinical & Experimental Research.
A study of rats conducted at Texas A&M University indicates that nicotine levels regularly achieved by human smokers can reduce the amount of alcohol that reaches the bloodstream. The finding has implications for the many who smoke while drinking alcohol.
"Smoking and drinking typically occur simultaneously," said physician Wei-Jung Chen, the study's lead author. "It's a very common phenomenon."
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Chen's team studied the effects of combining smoking and drinking by administering adult rats a standard dose of alcohol and various doses of nicotine ranging from zero to 6 milligrams per kilogram of body weight.
When they monitored the rats' blood alcohol content (BAC), they discovered that a higher nicotine level correlated to lower BAC. Blood alcohol level seemed to decrease in a dose-dependent fashion: At the highest amounts of nicotine, the level of alcohol in the rats' bloodstream was 50 percent lower than when the rats didn't receive nicotine.
In a follow-up experiment, the researchers determined that BAC only decreased when alcohol was ingested, not when it was injected. The finding indicated that the mechanism by which nicotine affects BAC involves the stomach and not the blood itself.
"The nicotine actually can decrease the rate of gastric emptying," Chen said. "If you have nicotine on board, [alcohol] will stay in your stomach a lot longer."
The stomach contains an enzyme called alcohol dehydrogenase, which breaks down alcohol. If alcohol remains in the stomach, more of it can be broken down, meaning less passes on to the intestines, where alcohol is absorbed into the bloodstream.
"I hope people won't interpret that as a good thing," Chen said, cautioning that nicotine's ability to keep BAC low could lead to risky behavior, prompting people to feel like they can knock back a few more drinks before leaving the bar.
Even if it never makes it into the bloodstream, whatever alcohol is consumed must be metabolized. The metabolic byproducts of this process are aldehydes, toxic chemicals that cause a wide range of alcohol's effects, including flushed face, hangover and tissue damage.
"[People] can't just use blood alcohol content as an index of the damage they're going to have," Chen said.
Not only might cigarettes prompt more drinking by lowering blood alcohol levels, said psychologist Saul Shiffman of the University of Pittsburgh, but drinking actually seems to spur smoking.
"When people are drinking," he said, "they're more likely to smoke."
Some of that association, Shiffman said, is psychological—resulting from lowered inhibitions and a conditioned association between cigarettes and bars or drinking—but some is pharmacological: A 2004 study from Duke University suggests that even small amounts of alcohol can intensify the pleasurable effects of nicotine.
"There's some evidence that smoking is more rewarding when you've had alcohol," Shiffman said. "It's a self-perpetuating phenomenon."