Feb. 15, 2000 (Atlanta) -- The common antacid medication Zantac (and the generic equivalent, ranitidine) can significantly increase blood alcohol levels and impair driving ability, shows a new study in the American Journal of Gastroenterology.

"The effect was striking," says author Charles Lieber, MD. In a three-hour test period, conducted under conditions similar to social drinking, the study showed that ranitidine can increase blood alcohol content by 38%. Levels reached in the study exceeded the legal drinking limit -- and the effects lasted up to two hours after drinking stopped.

Lieber's previous studies have shown that a similar medication, Pepcid (famotidine), had little effect on blood alcohol levels. Studies of ranitidine showed that it also had little effect -- but was only tested with one small drink.

"But, of course, social drinkers just don't drink one little drink, they drink several. In this study, we showed that if you do that after taking ranitidine, there's a cumulative effect, and it's quite significant. The blood levels impair driving function. People should be warned that when they drink moderately, they would find themselves driving home somewhat impaired. We felt this was an important point. In some countries, like Denmark, there's a warning label, but we don't have that yet," he tells WebMD. Lieber is professor of medicine and pathology at Mt. Sinai School of Medicine in New York and chief of the Alcohol Research Center at Bronx Veterans Affairs Medical Center.

In this study, Lieber and colleagues first screened 12 volunteers to find those who were able to process alcohol normally. Up to 30% of healthy people actually develop higher blood alcohol levels after drinking due to differences in their livers.

To simulate a social situation, the remaining nine volunteers were first given a standard breakfast, then were given four 10-ounce drinks at 45-minute intervals (potato chips were also provided during the drinking period) and blood levels were frequently measured. For the next week, each volunteer then took 150 mg ranitidine (comparable to two Zantac) daily, and the test was then repeated. That time, blood levels were higher after each drink -- high enough to significantly impair driving or judgment.