How will you celebrate St. Patrick’s Day and Cinco de Mayo, notorious for copious consumption of booze? If your plans include settling into a bar stool and chugging green beer on St. Pattie’s Day, or slurping margaritas while donning an oversized sombrero during Cinco de Mayo, you may first want to recall how your personality morphs after a few drinks too many.

WebMD talked to the experts to find out what’s to blame for booze-related personality and behavioral changes, and whether it’s possible to tame that other -- sometimes ugly -- persona that has a habit of rearing its head shortly after the drinks start flowing.

Are You a Risky Drinker?

The Angry Drunk

For many people, alcohol creates an overall sense of happiness and comradery. But in others it has the opposite effect.

For some, “alcohol is like fueling a fire,” says Dominic Parrot, PhD, assistant psychology professor at Georgia State University.

This reaction is not an inevitable reaction to alcohol consumption, experts believe. “Lots of people drink a lot, but not a lot of people become angry and aggressive,” Parrot tells WebMD.

Parrot recently conducted a study to examine just who is at risk for starting a bar brawl. Here’s what he found: “People who possess aggression-promoting personality traits are the most susceptible to alcohol’s effects on aggression.” In other words, if you tend to be a hothead when sober, alcohol will ratchet up the likelihood that you’ll want to punch the first guy who smiles at your date.

Why does alcohol trigger an aggressive response in someone who ordinarily can squelch aggressive tendencies? “We believe alcohol disrupts cognitive functioning, making us unable to look at different problem-solving options,” Parrot suggests.

Moderate Drinking OK for Most People

When Drinkers Get Depressed

While most people report increasing feelings of friendliness when they consume alcohol, a small percentage -- 2 percent, according to one national survey -- wind up crying into their drinks while everyone around them is dancing on tabletops.

Why does alcohol, reported by many drinkers as a way to unwind and relieve stress, have just the opposite effect in others? No one knows for sure, but researchers do know that for some people, drinking increases responses to stress, sometimes manifesting as tears flowing into beer. Although the evidence is inconclusive, some scientists suggest that this depressive effect may mean a greater susceptibility to problem drinking. For others, the explanation may be simpler: the loss of inhibitions that comes after a few drinks may simply release the drinker’s pent-up feelings.

Alcohol Problems Up in College Students

Alcohol and Promiscuity

While some drinkers look for fights, others look to satisfy feelings of love -- or, more precisely, lust. “Our culture tells us that alcohol and sex go together, yet it is illegal to use alcohol to facilitate sex,” says Aaron White, PhD, a psychiatrist at Duke University Medical Center.

Licentious behaviors linked to drinking range from mildly annoying to downright dangerous. Looping an arm around the shoulders of an acquaintance is one thing. Acting like a sexual predator is another thing altogether, and can escalate into an act of violence. White calls alcohol “the No. 1 date-rape drug.” And he blames not only the perpetrators, but our culture at large.

“We don’t view people as responsible when they’ve been drinking,” White tells WebMD. “We live in a culture in which alcohol is used as an excuse for behaviors.”

Understanding Alcohol Abuse -- Treatment

Cultural Influences on Drinking

That’s not the case universally, says Stanton Peele, PhD, adjunct psychology professor at New School University and author of the book Seven Tools to Beat Addiction.

“In some cultures, intoxicated behaviors are heavily disapproved of. When people become drunk they don’t act the same way [that Americans do],” he says. He cites southern European countries, where alcohol is typically introduced early, within the context of family gatherings. “It demystifies alcohol and, as a result, you don’t see so much acting out. Instead, drinking alcohol is associated with meals and convivial good times,” Peele tells WebMD.

In most U.S. households, parents take a vastly different approach. “We tell young adults never to drink. It gives them a tremendous excuse to act out when they do drink,” Peele says.

A recent U.S. survey of 644 women aged 17 to 35 conducted by the American Medical Association backs this theory. When asked if they use drinking as an excuse for outrageous behavior, 74 percent responded in the affirmative.

Shifting Ideas About ‘Normal’ Consumption

Is it possible to change the widely held belief that it’s OK to act stupid and irresponsible when drinking? Since it’s a culturally accepted norm among many young adults, it stands to reason that such a change would require a “shift” in thinking about what’s normal. That’s exactly what social-norms marketing attempts to do.

Social-norms marketing identifies people’s misperceptions about their peers’ behavior and then educates them to correct these misperceptions. It’s a concept that, when applied systematically, has effectively reduced heavy drinking and related harm at college campuses in the U.S.

Michael Haines, director of the National Social Norms Resource Center at Northern Illinois University, explains the logic behind social-norms marketing. “If I think everyone’s getting drunk at a pub crawl, I’m going to, too,” he says. “False norms create imaginary peer pressure.” In a study of more than 76,000 college students, Haines and associates found that more than 70 percent of college students overestimate the drinking norms at their school. Why is that relevant? Because these same researchers also found that students' perception of their campus drinking norm was the strongest predictor of personal alcohol consumption.

Misperceptions About Alcohol-Induced Behavior

When it comes to alcohol consumption and behavior, misperceptions abound -- and not just among the young and inexperienced. The most dangerous ones have to do with people underestimating their own level of incapacitation.

This all-too-common phenomenon was clearly illustrated by psychology professor Kim Fromme, PhD, who had a group of moms visit her “simulated bar laboratory” and drink as much as they wanted for a few hours. Fromme, a professor at the University of Texas at Austin, found that many of the subjects believed they were “OK to drive," even after consuming several drinks. After imbibing, the subjects expressed shock at how miserably they failed a simple balance test that required them to walk in a straight line.

“The psychoactive effects of alcohol are first evident at 0.05% blood alcohol. That’s one to two drinks for most people. Judgment and reason are the first abilities to be negatively affected by alcohol. That said, it’s too late for people to decide whether they’re ‘OK to drive’ after they’ve already begun drinking,” Fromme tells WebMD.

The same goes for any other behavior. After tossing back a few drinks, it’s probably too late to decide whether your actions are acceptable -- particularly when they take place within an environment that condones irresponsible behavior as an inevitable part of drinking.

“It’s amazing how much people really do want to conform,” White says.

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By Elizabeth Heubeck, MA, reviewed by Louise Chang, MD

SOURCES: Dominic Parrot, PhD, assistant psychology professor, Georgia State University. Aaron White, PhD, psychiatrist, Duke University Medical Center. Stanton Peele, PhD, adjunct psychology professor, New School University; author, Seven Tools to Beat Addiction. Michael Haines, director, National Social Norms Resource Center, Northern Illinois University. Kim Fromme, PhD, psychology professor, University of Texas, Austin. News release, American Medical Association. Parrott, D.J. Alcoholism: Clinical and Experimental Research, 2003; vol 27: pp 937-945. Sayette, M.A. Alcohol Research and Health, 1999; vol 4: pp 250-255. Perkins, H.W. Journal of Studies on Alcohol, 2005; vol 66: pp 470-478.