Are you more drunk than you think?

Laura Allahverdi thought nothing of getting into the driver’s seat one evening in October 2004 after having two vodka cranberries.

"I didn’t feel intoxicated at all," says the 29-year-old life coach, who waited two hours after drinking before leaving the bar. Heading home in Suffolk County, N.Y., she was surprised when a police officer pulled her over. When he requested that she take a Breathalyzer test, Allahverdi complied—and learned that she’d registered a blood-alcohol concentration (BAC) of a little over 0.08, the legal limit nationwide.

"He handcuffed me and put me in his car," she says. "I couldn’t believe it." Just two drinks cost her a night in jail and an automatic license-suspension.

Like Allahverdi, you’d probably never dream of getting behind the wheel if you were drunk. Yet the number of women arrested for driving while intoxicated increased by 31.5 percent between 2000 and 2009. Now, more than ever, we’re drinking socially, and not just on a Saturday night out; we’re reaching for that Pinot or Pomtini to liven up book clubs and our kids’ afternoon play dates. Meanwhile, study after study tells us drinking may protect against illnesses like heart disease and diabetes, making that nightly glass of wine feel like a good-for-you habit.

While experts agree that moderate drinking may have benefits, they also note that women have to be especially careful about how much they consume. Alcohol goes wherever there’s water in your body—your tissues, your organs, your bloodstream. Generally, the more you weigh, the more water you contain, and the more quickly and/or easily alcohol is diluted in your system, meaning men (who tend to be bigger) will feel its effects less than women.

Women also have a higher fat-to-water ratio than men do. So a 150-pound man holds more water than a 150-pound woman; after one drink, the woman will have a higher concentration of booze in her blood. That leads to greater intoxication. And her liver has to work harder to metabolize that alcohol, prolonging her buzz.

"For every drink a woman has, it’s the equivalent of a drink and a half for a same-sized man," says Dr. Harold Urschel, author of Healing the Addicted Brain and chief medical strategist at Enterhealth Ranch substance-abuse center in Dallas.
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When one drink is really two...or five
One standard drink equals about 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of liquor—but there may be way more in your glass. Here’s why:

Different beers and wines contain different measures of alcohol by volume (ABV).
The ABV for beer is generally about 5 percent, but it can range from 3.5 for an Amstel Light to 6.8 for a Sierra Nevada Celebration Ale. Specialty brews can pack a greater punch: Samuel Adams Triple Bock has an 18 percent ABV. A bottle of wine can range from as little as 9 percent ABV to as much as 15 (most fall between 12 and 14). Check labels or ask your server to find out your drink’s ABV.

A pint doesn’t always equal a pint.
Drinking at a British or Irish pub? You might get served an imperial pint, which holds about 19 ounces. An American pint holds 16.

A glass of wine might really be more.
Wine glasses today can hold as many as 28 ounces—meaning you could get up to five servings of vino at once if you’re filling that goblet to the rim.

Mixed drinks are a mixed bag. Ordering a gin and tonic? There’s no way to tell if the bartender had a heavy hand with the gin. And drinks with multiple types of booze may contain three or more servings of alcohol.

BYOB (Bring Your Own Breathalyzer)
An increasing number of bars and restaurants are keeping Breathalyzers on hand, offering customers a chance to gauge their sobriety before getting behind the wheel. But you can also buy your own for as little as $30 at online retailers like amazon.com.

"It’s a great idea to curtail drinking and driving," says Tony Corroto, a standardized field-sobriety testing and drug-recognition expert instructor for the National Highway Traffic Safety Administration. These inexpensive gadgets might not be as sensitive as the professional models used by law-enforcement officials, Corroto says, but the good news is that in most instances, an imperfect Breathalyzer will potentially overestimate your BAC—meaning you’re more likely to play it safe by calling a cab.

But isn't booze good for me?
Yes, drinking does have documented health benefits. Moderate consumption of any type of alcohol can increase your HDL, or good, cholesterol by about 12%, a 2001 science advisory by the American Heart Association suggests. Furthermore, men and women who drink moderately have a 30% lower risk of developing type 2 diabetes, according to a meta-analysis published in Diabetes Care. And that’s just scratching the surface of research on this topic.

The million-dollar question: What does "moderate" drinking mean? Just one drink a day, especially for women, says Eric Rimm, an associate professor in the departments of epidemiology and nutrition at Harvard School of Public Health. Having two or more drinks a day can increase your risk of developing breast cancer by as much as 41%, according to a 1998 analysis published in the Journal of the American Medical Association; even that moderate one beverage per day is associated with a 10 percent bump in risk, Dr. Rimm says.