Alcohol's ability to increase people's pain threshold is one reason that drinking also leads to more aggressive behavior, a new study suggests.
Researchers found that the less pain that study participants felt after drinking an alcoholic beverage, the more pain they were willing to inflict on someone else.
"We've all heard the idiom 'I feel your pain,'" said study co-author Brad Bushman, professor of communication at The Ohio State University.
"But if intoxicated people can't feel their own pain, they might be less likely to feel empathy when others feel pain, and that could lead them to be more aggressive."
The study was published recently in the Journal of Studies on Alcohol and Drugs.
This study used an experimental design that has been used in research studies since 1967 and has been approved for use in humans in this study and others.
This new research involved two independent laboratory experiments, one with 543 participants and the other with 327 participants, all of whom reported consuming 3-4 alcoholic beverages per occasion at least once a month. They were recruited by newspaper advertisements and paid $75. The methods for the two experiments were identical.
After giving informed consent, participants were given 20 minutes to drink an alcohol or placebo beverage. The orange juice beverages looked identical so participants wouldn't know which one they got. For the placebo drinks, the researchers put a small amount of alcohol on the top of the orange juice and sprayed the rim of the glass with alcohol so that it tasted like an alcoholic beverage.
After drinking the beverage, each participant received one-second electrical shocks to two fingers on one hand. The researchers increased shocks in intensity until the participant described the shock as "painful." That was labeled the participant's pain threshold.
They then participated in an online competitive reaction time task in which the winner could deliver a shock to the loser. The shocks ranged from 1 (low) to 10, which was the level the participant rated as "painful." Participants could also choose how long the shocks lasted.
In reality, there was no opponent and the researchers randomly declared the participant the "winner" in half of the reaction time tasks. The purpose was simply to see if those who drank the alcoholic beverage would be willing to deliver stronger and longer shocks - and whether a higher pain threshold had an impact.
Results showed that for those drinking alcohol, the alcohol increased the level at which the shocks became painful to them. And the greater their tolerance for physical pain, the greater their level of aggression in terms of the intensity and length of shocks they were willing to deliver to the opponent.
Those who drank the placebo drinks weren't as aggressive in their response, partly because their pain threshold was generally lower than those drinking alcohol, Bushman said.
"In other words, they were still able to feel their own pain - and didn't want to inflict pain on others," he said.
"There are many reasons that intoxicated people are more likely to intentionally hurt others, but this research suggests pain tolerance is one possible reason."
Bushman noted that the people who drank alcohol in this study had blood alcohol concentrations averaging between 0.095% and 0.11%. That's slightly above the legal limit in most states, which is 0.08%.
"The effects of alcohol on pain tolerance may be higher for those who drink more than what they did in these experiments," Bushman said. "That may make them even more willing to be aggressive against others."
Co-authors on the study were C. Nathan DeWall of the University of Kentucky, and Peter Giancola, a licensed clinical psychologist in Montreal.
The research was supported by the National Institute on Alcohol Abuse and Alcoholism and the National Center for Research Resources.
