(FORTUNE Magazine) – Considering that the stuff has been around for at least 6,000 years, and that historians think it may have been invented even before bread, and that 70% of the adult American population uses it, and that it once accounted for half the police activity in the country, and that the federal government spends about $200 million a year studying it, the ignorance, confusion, and self-delusion surrounding alcohol is absolutely stupendous.

Take the news that alcohol consumption has dropped steadily over the past 15 years. It's true. There has been a big shift in attitude about drinking since the 1970s, when a quarter of the New Yorker magazine's cartoons portrayed someone with a drink, and the three-martini lunch was very much alive. Nowadays you can drink Perrier all night at a party and guests don't wonder if you're a recovering alcoholic. The cocktail hour before corporate board meetings is a relic, and eyebrows go up invisibly if you order wine at a business lunch.

From which it is tempting to conclude that demon rum just isn't much of a problem anymore, except for grizzled old men living under bridge abutments, right? Sorry, bud. It seems most of that slowdown in drinking occurred among people who weren't very interested in alcohol anyway. The portion of the population deemed to have abused alcohol in the past year--for example, 14% of men in their 30s and early 40s, and 4% of women--hasn't changed much.

And as Drew Lewis, chairman of the Union Pacific railroad, can attest, education, income, and a spectacular career don't offer much immunity against the perils of alcohol. His problem controlling alcohol surfaced last year right in the middle of a battle to acquire Santa Fe Pacific, a rival railroad, in a hostile takeover. He screwed up, so he bravely and publicly stepped down for five weeks to enter a treatment center.

Wow, you say. This alcohol sounds like powerful stuff. How can I tell, without getting a sermon, if I'm at risk, or if my after-work Manhattans will leap up and bite me just when I'm trying to acquire a railroad? Listening to warnings about alcohol from recovering drinkers often has that overwrought flavor, like getting lectures on firecracker safety from two-fingered munitions handlers. Diagnose-it-yourself questionnaires seem hopeless too, with questions that often sound like: "(1) Have you ever tried alcohol? (2) Are you frequently surprised to find yourself waking up with a splitting headache in a Las Vegas hotel room, surrounded by gerbils and naked showgirls? If you answered yes to either of these questions, you may already be an alcoholic!"

It turns out, though, that researchers have recently come up with surprising predictors of who is at risk for alcoholism and when it is likely to surface. They may have spotted more than one variety of alcoholism, and they have developed plausible theories of why some people have a stronger urge to drink than others.

If you have crossed over the line to join the huge mass of other competent, successful people who have a booze problem, you will be relieved to know that attitudes toward alcoholism have changed a lot. Twenty years ago it was seen as the product of personal weakness and incurable personality flaws. Incredibly, some psychiatrists even argued it was a form of suppressed homosexuality (drinking is oral, see, and .). But as 40-year-long studies of Harvard students and kids from inner-city Boston have determined, there's no clear-cut future-alcoholic personality. In fact, the people who seemed most likable and well adjusted when young turned out to be a tad more likely to run into trouble.

There is no litmus test for borderline alcoholism, and if you're interested in finding out exactly how much you can drink without technically qualifying as a person with a drinking problem, don't bother. The only important judge of whether you're an alcoholic is yourself, because that's who has to correct the problem, and as everyone knows, alcoholics are fabulous at coming up with reasons why their excessive consumption doesn't mean they qualify. It's part of being a salesman, I can hold it, I can stop anytime, etc. The simplest definition is almost a tautology: If alcohol is causing you problems, and you keep drinking anyway, you've got a problem with alcohol.

Don't gauge yourself by whether you're having alcohol-related difficulties at work. Says George Vaillant, the professor of psychiatry at Harvard medical school who runs those studies of Harvard students: "The last symptom before you're sleeping in the Bowery is trouble at work. Everything else occurs first." For a variety of reasons, executive and professional types probably can hide alcohol abuse from co-workers better than most. Much earlier indicators: spats with the wife, falling asleep and ignoring the kids, warnings from your doctor that certain liver enzymes are high, gastric trouble, sexual dysfunction, car accidents.

You want numbers anyway. Ounces, probably. First, a not-so-amusing observation that researchers have made when they ask people how much they drink: The numbers don't add up. Of the 447 million gallons of pure alcohol consumed annually in the U.S.--that's equivalent to more than 500 cans of beer per adult--mysteriously, 40% to 60% cannot be accounted for in surveys. Some of that is because pollsters didn't quiz the folks living under the bridge abutments. But more often, people report their most common drinking pattern--what they have on Mondays, Tuesdays and Thursdays--and ignore poker night on Wednesdays, happy hour on Fridays, all-day sipping and parties on Saturday, and six-packs with football on Sundays. It adds up very quickly, and a lot of people who find themselves neck deep in trouble with booze are stunned to realize how much they really consume.

These are the numbers, and be careful how you use them. First, experts do not define a "drink" as a large water goblet brimming with scotch. A drink is a half-ounce of ethanol, the amount in one 12-ounce beer, an ounce and a half of 80-proof liquor, or four ounces of wine.

Two drinks a day are almost always okay for a healthy adult male. For many it's downright pleasant, in fact. One of alcohol's great charms is that it is an excellent, fast-acting muscle relaxant, something like Valium. If you're tense from work or from three hours of driving, alcohol, in those doses, will make you feel better, unless you're allergic. Bigger doses won't do much more for your tight muscles, though many people keep trying. And, of course, alcohol reduces inhibitions and makes people feel expansive. In small doses it's okay--you may be more likely to chat with your spouse than curl up on the sofa and sulk about your day. People who consume up to two drinks a day actually reduce the risk of heart disease and live longer than teetotalers and serious boozers. (Downing two belts of vodka on an empty stomach and zooming home on a rain-swept, winding road, however, will not extend your life.)

Women, even large women, should not drink as much as men. Both men and women have an enzyme in their liver, alcohol dehydrogenase, that breaks down alcohol in their blood. But men also have the enzyme in their stomachs, where it breaks down 30% to 40% of alcohol before it causes a lot of trouble. Women do not.

Three and four drinks a day are tolerable for a large man who doesn't have to drive or perform, but dumb. Motor control and inhibitions keep declining with bigger doses, so you'll get sloppy. They add calories (by volume, vodka and ice cream are about equal in calories), may make you drowsy or snappish, and slightly increase the risk of illness. Five a day, even once a week, counts as "frequent heavy drinking" and means you're getting pretty plastered pretty regularly. Eight drinks in a day at least weekly is very serious. Lorraine Midanik, a researcher at Berkeley, says that kind of drinking is strongly associated with true dependence on alcohol.

Heavy and binge drinkers are more likely to have car accidents and pull really dumb stunts in public. Steady, daily drinkers are more likely than bingers to have medical problems. In France problem drinkers rarely get bombed (the only alcoholics are tourists, the French like to brag). But they consume liters of red wine over the course of a day and the cirrhosis rate is twice that of the U.S.

As drinking customs from the 1970s reveal, though, gallons consumed is a far-from-perfect barometer of alcohol trouble. Jerry Della Femina, the advertising executive, describes the astounding days of the three-martini lunch. First off, they were huge martinis: six ounces of gin and a drop of vermouth, topped with a sliver of lemon "because olives took up too much room." And they were routine. "It was as much habit as anything," he says. "We'd do it without thinking or ceremony, like coffee." Sometimes the drinking involved more than three martinis. Della Femina recalls lunches in which he and three other people also drank two bottles of wine and finished their meal with some scotch. How could any executive function, much less compete, after all that? "It wasn't a problem," he says. "It wasn't just the advertising business where people drank like that. Everybody was in the same condition, so nobody noticed or cared. Every afternoon in New York this fog--this big alcoholic fog--rolled in over the city."

But all that drinking didn't make everyone an alcoholic. For reasons Della Femina can't fully explain, and without his realizing it at the time, that kind of heavy drinking faded out of fashion in the early 1980s. He suddenly realized a few years ago that he and his friends had gradually shifted to nonalcoholic lunches. For old times' sake, he tried recreating the three-martini lunch. "After the first one, my head was spinning. If I'd tried to have three, the last one would have arrived at the same time as the ambulance." He concludes that his tolerance declined, and his desire to be sober increased. "The only people who kept drinking were the people who had a problem with alcohol."

Robert was supposed to make partner, but there was a bear market on Wall Street that year in the 1970s, and all promotions were canceled. As a consolation prize, he was given a membership in an exclusive club downtown, where his food and drinks were free. At the same time his job expanded. He was responsible for operations over a large portion of the company. He'd been comfortable in the previous assignments, but this one came with a lot of pressure. Eventually he found himself drinking every day at lunch.

"After a while, it was two or three martinis. I'd always try to arrange lunch with friends. If that didn't work, I'd go by myself. Funny. If there was a staff meeting called for lunchtime, it wouldn't bother me that I couldn't drink. But otherwise, I always did. About ten years ago my doctor started telling me my liver readings were high, that I had high blood pressure and my heart was slightly enlarged. I was drinking two or three bottles of vodka a week. I tried stopping at least six times, but the longest I went was two months. I was doing very well at work. I wound up very high in the organization. Drinking didn't affect my performance. But I was extremely impatient with people on the staff-demanding, bordering on abusive.

"About five years ago I was put in charge of an extremely demanding project. I also got responsibility for all work on the stock exchanges. There is an unwritten rule on Wall Street that nobody on the floor drinks until the market closes. Meanwhile, my compulsion to drink was increasing. Because of that stock exchange custom, and because I was in my 60s and worried that drinking would ruin my life after retirement, I decided I had to quit. I talked to my doctor and she helped me get into Alcoholics Anonymous."

Why did Robert find martinis so addicting when Della Femina did not? Parents get some blame, but not in ways you'd expect. It has been obvious for centuries that children of alcoholics are about four times more likely to become alcoholics than kids of parents who don't have drinking problems. But everyone assumed children learned this behavior by watching mom or dad get drunk. Not so. Dr. Donald Goodwin, professor emeritus of psychiatry at the University of Kansas Medical Center in Kansas City, studied male children of alcoholic fathers in Denmark who had been adopted very young and raised away from their biological parents. It turned out that 20% wound up as alcoholics--the same percentage as kids who grew up with alcoholic fathers.

Exactly what alcoholic parents pass along to their children isn't clear, but one important trait is the opposite of what you might expect. Children of alcoholics are much more likely to have a high tolerance for alcohol. And those two-fisted drinkers who could put their friends under the table from the very beginning, researchers have discovered, are actually at much greater risk than those who get dizzy or sick or drunk on a few drinks.

Beginning about 17 years ago, Dr. Marc Shuckit, of the veterans' hospital in San Diego, gave controlled doses of liquor to more than 450 college students. About half were the sons of alcoholics, and half were not. Shuckit found that roughly 40% of the students with alcoholic fathers had low reactions to alcohol, based on several measures, while only 10% of the other students could hold liquor well. Ominously, he found in follow-up studies that 60% of the sons of alcoholics who could drink a lot without much effect went on to become alcoholics. Only 15% of the students who got drunk quickly became alcoholics.

Why? Nobody knows for sure. Shuckit says he can't find evidence that the hollow-leg students had personalities different from the easily sloshed ones'. It seems, though, that people who get drunk easily simply drink less. They are less likely to consume so much that their bodies adapt to the high doses and need ever bigger amounts to get high. If they drink a lot with their fraternity brothers on Friday, they're too sick on Saturday to do it again. The two-fisted drinkers, admired in some perverse way by their peers for their prowess, are ready to party again on Saturday. They may gradually develop a circle of other high-tolerance friends, where everyone is drinking two or three times as much as a normal person just to get the same effect.

In retrospect, Mike Neustadt realizes he had an enormous tolerance from the beginning. In college he could outdrink older students. "It made me think I was a heavy hitter--I could drink with the big guys. But with high tolerance, there were fewer effects on my behavior that might have caused me to slow down. I got a false sense of control. I'd drive drunk friends home, I'd help people who got sick. My circle of friends changed. I needed friends to drink with every day."

It didn't hurt him at first. At 21, Neustadt was one of the youngest people ever to get a seat on the Chicago Board of Trade. Five years later he lost his job. "I got into some bad positions because of my drinking," he says. What bothers him as much as losing the job was the "ethical deterioration" that took place because of alcohol. He didn't steal or cheat, but the standards he set for himself declined. "When I first got that seat on the board, there was nothing in the world more important to me. Five years later I could say to myself, 'It's no big deal. I can always get another job.' " Alcohol was more important.

Do alcoholics develop a greater appetite for drink from their first taste than the rest of the population? It certainly seems so to people close to the matter. When former Senator George McGovern's 45-year-old daughter was found dead in the cold this winter in Madison, Wisconsin, after battling alcoholism for most of her adult life, he said she'd had a craving for alcohol almost immediately after trying it as a teenager. Scientists aren't so sure, though some think they have identified two conditions that could be predictors of later problems: antisocial personality disorder, or ASPD, and attention deficit disorder with hyperactivity, or ADD-H. The first describes incorrigible schoolyard bullies who are robbing gas stations by 14. They are highly impulsive and undeterred by punishment. The ADD-H types aren't so malevolent but can be extremely unfocused, energetic, and impulsive.

Both types are in danger of intense drinking problems that surface in their teens and 20s, prompting some researchers to argue that there is an "early onset" form of alcoholism. Others disagree, pointing out that these conditions run in families and may predispose certain people to get into trouble with a lot of things, including alcohol.

Still, even though there is no conclusive proof, it seems likely that people who become alcoholics do crave the stuff differently. Dr. Joseph Volpicelli, at the University of Pennsylvania Medical Center, says most normal people will have a few drinks and lose the desire for more. But people with alcoholism in both generations preceding seem to find their craving increases after three drinks. "I call it the corn-chip effect," says Volpicelli. "Give me two or three corn chips, and suddenly the rest of the bag becomes irresistible. For some people, alcohol is that way." He thinks receptors in the nervous system for naturally occurring opiate-like hormones called endorphins may be the culprit. For some, small doses of alcohol stimulate production of a bit of these endorphins. When they wear off, the opiate receptors are jangling for more, creating what feels like a craving for alcohol.

Stress may have a similar effect, says Volpicelli: The body produces feel-good endorphins while under stress, but when the stress is gone and the endorphins wear off, those corn-chipped opiate receptors are still hungry, begging for a belt of Old Overshoe. Conceivably, says Volpicelli, colossal stress--like a few years in Vietnam--might fry even a normal person's opiate receptors, creating long-lasting cravings. The link between opiates and alcohol has long been suspected, observes Dr. Goodwin in his engaging book, Alcoholism: The Facts. Volpicelli says a compound called naltrexone, which blocks the craving for opiates, also seems to work with alcohol. Marketed under the name Revia, it reduces relapses among recovering alcoholics.

And no, depression doesn't lead to alcoholism, at least not among men. Many alcoholics eventually become profoundly depressed, but that seems to be a result of the depressant effect of the alcohol itself as well as the mess they've made of their lives, and it usually goes away within a few weeks of recovery. There are lots of people who are genuinely depressed and who are alcoholics, but that's because they are unlucky enough to have both problems. Donald Rosen, head of the Professionals in Crises program at the Menninger Clinic in Topeka, says antidepressants don't help alcoholic men stop drinking unless they have a depression as well.

If you're a man and not an alcoholic by the time you're 45, you almost certainly will never be. (All you 46-plus men who just went "whew, now I can get drunk whenever I want," are probably already in trouble.) Says Goodwin: "The typical white male alcoholic begins drinking heavily in his late teens or 20s, drinks more throughout his 20s, starts having serious problems in his 30s, has his first brush with hospitalization in his middle to late 30s, and is clearly identified by himself and others as an alcoholic--a man who cannot drink without trouble--between 40 and 50."

If you have a drinking problem, chances are fairly good that your boss and most coworkers don't know how serious it is. "Successful executives are street smart as well as smart smart," says Joseph Califano, a former Cabinet Secretary and top corporate attorney who now runs an addiction research and education program with Columbia University. "If they're alcoholics, they don't drink in the morning. They use eyedrops to hide the red. They don't drink in front of the board."

Executives can hide in part because of the fuzzy descriptions of exactly what it is they are supposed to do. Few will return from a liquid lunch bumping into the furniture or forwarding a half-finished memo to the boss. "The impact isn't so much on the quality of the work done as the quantity," says Laura Altman, head of the behavioral health practice for Towers Perrin, an employee benefits consulting firm. "People who have several drinks at work go over and over their work, trying to eliminate errors that would give them away." They are likely to be irritable or abusive of co-workers. Often, the first on-the-job alarm bell for an alcoholic is a sexual-harassment complaint, says Jeffrey Speller, a Belmont, Massachusetts, psychiatrist who specializes in troubled executives.

Even if the exec does all his drinking at home, or binge-drinks on weekends, it eventually has an effect. "There's slippage,'' says Gene Gaeta, head of AT&T's employee assistance programs. "Imagination and creativity are affected. They aren't producing the ideas they once did. It takes a while to spot."

And sometimes, you screw up big time, and publicly.

Drew Lewis, chairman of Union Pacific, the nation's biggest railroad, had been struggling off and on with alcohol for years, says a close acquaintance. But last year the problem was getting worse. After a few drinks before a speech in Philadelphia, he joked about buying Conrail. For people who knew him, it was typical of his dry humor, but some in the audience thought he was tipsy. A few weeks later he had a car accident and required 11 stitches on his head.

In June two rival railroads, the Burlington Northern and Santa Fe Pacific, announced plans to merge. Robert D. Krebs, head of Santa Fe, reported later that Lewis promptly called him and said he wouldn't oppose the merger. Then, after months of deliberation, Union Pacific made an offer to buy Santa Fe. It was rejected. On October 5, Lewis called Krebs, insisted on a meeting, flew that day to Santa Fe headquarters near Chicago, and met with him. Lewis had some drinks before the meeting. Krebs rejected UP's offer of $17.50 a share. As Lewis was leaving the meeting, Lewis suggested $20 a share. News of Lewis's second offer stunned colleagues, who were not expecting it. Board members were even more stunned, because they had not authorized it. When he came back from the meeting with Krebs, Lewis admitted to friends on the board that he had a drinking problem. Then he immediately stepped down to enter a treatment facility. He was back on the job after five weeks but declined to speak of his experience to Fortune, explaining that treatment counselors urged him to remain silent for a year.

Some board members knew of Lewis's drinking problems, others thought he was a teetotaler. "I never saw Drew take a drink or be incapacitated," said one, "but apparently, in talking to people in the course of the tender offer that day, it was clear he was not sober." One board member once offered him an expensive bottle of wine for Christmas. He replied that he didn't drink wine but would accept it and give it to his wife.

A few days after he left for treatment, the UP board and top executives met and decided to make an announcement about Lewis's treatment. Some were concerned that Lewis's alcoholism was a significant business matter that had to be revealed to Santa Fe and Union Pacific shareholders; some thought it should be announced because it would be impossible to hide his absence; some viewed it matter-of-factly, as a medical condition to be mentioned without fanfare or embarrassment.

Lewis learned of the announcement while in treatment. He told a UP colleague his first reaction was "Holy smackers, do we have to do this?" But he got hundreds of letters from well-wishers, including several who said he had inspired them to quit too. He attends 12-step group meetings with other recovering alcoholics virtually every day, says a UP executive, and even prepares a list of 12-step meetings he can attend while he is traveling. In February, Union Pacific announced it was no longer seeking to acquire the Santa Fe.

What is it like cutting down or giving up drinking? It varies, of course, but generally it's tough. If you're up around four or five drinks a day, you're probably not physically dependent. That kind of urge to drink is largely habit, or situational, says Dr. Gene Ondrusek, a consultant at the Center for Executive Health in La Jolla, California. "You've come to associate certain situations, like getting home from work, having a meal, or watching football, with drinking. "

If you have a pitcher of martinis with the missus before you even take off your suit, change your routine. Don't stand next to the refrigerator biting your nails and thinking about gin. Walk the dog, build a fire. Do something to create a different pattern of cues. It will be uncomfortable for a while, but you should be able to cut way back or stop. "A lot of executives don't have good relaxation skills," says Ondrusek, "so they find alcohol a good tension reliever."

People with severe drinking problems who can't control their drinking once they start--the classic definition of an alcoholic--usually have to stop altogether. There isn't much consensus on the best way to accomplish that. Some quit on their own. Others go to treatment centers or join groups like Alcoholics Anonymous. Neither approach guarantees success. One study found that a year after treatment one-third were still abstinent, one-third had cut down, and one-third were drinking as much as before.

But for some, treatment centers are invaluable. They typically offer medical care--the first week of no drinking can produce withdrawal symptoms--and lots of group therapy and counseling. Much of it is aimed at educating people about alcoholism, getting them to realize that they really can't control their drinking like most people, and teaching them coping skills. AA helps people see and admit their problem too, and also provides a support group that many people need. Often they feel intense loneliness because they've had to give up their drinking buddies. Such emotions as anger or depression or insecurity that the alcoholic damped down for years by drinking may surface, causing problems in relationships with family and friends.

The urge to drink really does diminish over time. If you manage to kick it, you will be secretly admired by everyone around you, except for a few discomfited alcoholics. You will bounce back surprisingly well--it's a myth that drinking permanently hurts your intellect and creativity--and will return undiminished. You can declare, as Drew Lewis has, "I've left my guilt at the treatment center. I'm back."