By Gabrielle Glaser

The film adaptation of Paula Hawkins’ bestseller, “The Girl on the Train,” was last weekend’s top earner, but it opened to mixed reviews.

[Warning: slight spoilers ahead.]

It’s told mostly through the bloodshot eyes of Rachel (played by Emily Blunt), whose husband Tom (Justin Theroux) left her after she couldn’t conceive a baby for Anna, (Rebecca Ferguson) a pretty blond who could. Rachel, who’s lost her job, too, takes a train into Manhattan every day from a town on the Hudson River past her old house, where she often spots Tom, Anna, and their baby. She also sees another house where Megan (Haley Bennett), another pretty blond, lives. Rachel drinks—a lot—pouring fifths of vodka into a giant plastic gym bottle with a built-in straw, and she tosses back martinis at a bar. That’s a lot of vodka, and Rachel, not surprisingly, hardly remembers how she gets through the day.

One morning after a night of heavy drinking, Rachel wakes up with her hair and clothing plastered with blood. She has no idea what happened. Megan, she later learns, has gone missing, and Rachel—along with her absent memory—becomes embroiled in her mysterious disappearance. Rachel can’t recall her actions, but she’s ashamed and scared. What happened while she was drunk out of her wits?

I’m a journalist who’s written about health, especially mental health, for decades. Several years ago I noticed that American women were drinking more than ever before, and it became the basis of a book that also examined evidence-backed ways in which drinkers could get help.

The topic of women and alcohol always draws me, and I was curious how the film would depict blackouts. It wasn’t easy, probably because blackouts aren’t. The plot is convoluted, the narrative switches clumsily from person to person, and the timeline is so confusing that words flash on the screen to tell you where you are: four months ago, two months ago, last week—or maybe not. It’s hard to keep up.

This is, apparently, to indicate the difficulty Rachel has in keeping the dates straight because she’s so addled by booze. Reviewers call her an “alcoholic,” a word researchers have rejected for decades. They now use the somewhat clunky phrase “alcohol-use disorder,” which sensibly, denotes a spectrum, and not the binary “you-either-are-or-you-aren’t” alcoholic.

Rachel, who is definitely on the severe end, doesn’t feel she has a lot to live for, so she pretty much just…drinks. Because she’s a woman, everyone judges her harshly: her nasty ex, the town detective (played by Allison Janney), and certainly her ex’s new wife. Men who develop alcohol problems tend to get a lot more empathy.

I’m not a big drinker—I hate feeling out of control. But I did have what’s called a “brownout” my freshman year of college after polishing off a bottle of Cracklin’ Rosé. I spent most of the night throwing up, which I remember, but there’s a photograph of me clutching a box of Tide with glassy eyes that I don’t recall anyone ever having taken. It was scary, and my experience with really overdoing it ends there. Still, I’m drawn to what pulls people, especially women, to regularly go that far with their drinking.

Blackouts are clearly a thing: in 2015, there was a serious examination of the topic in popular culture. Hawkins’s book came out in January, and in July, Sarah Hepola wrote a bestseller called “Blackout: Remembering the Things I Drank to Forget.” A few weeks later, Amy Schumer’s film “Trainwreck” opened with her waking up in Staten Island next to a guy she doesn’t remember meeting.

So: how often do people black out? I spoke to Dr. Aaron White, an expert on blackouts and a senior scientific advisor to the director of the National Institute on Alcohol Abuse and Alcoholism. He had a simple answer to my question. “They’re disturbingly common,” he said.

Blackouts occur when a person is drinking, usually, but not always, to excess, because alcohol interferes with the receptors that record new experiences in the hippocampus, the brain’s memory center. Depending on one’s tolerance, how much one has eaten, and how hydrated one is, blackouts can be either fragmentary, sometimes known as “brownouts” or “grayouts,” or complete. White calls those “en bloc” blackouts, when the person who experiences them remembers nothing.

Hepola says they’re terrifying. “The blackout drinker lives with terror the moment he or she wakes up,” she said. “You ask yourself, ‘Am I alone in the bed? How did this pizza box get here?’ You have to do detective work on your own life.”

They are especially alarming for women, White said. Among the college students he’s studied for blackout research, he said, responses to them fall across rigid gender lines. “Males wanted to know what they did to the world,” he said, “But women were uneasy, and wanted to know what happened to them.” The notion of sex while a woman was too drunk to consent is particularly frightening.

Hepola described coming out of a blackout in a Paris hotel room while she was having sex with a man that she had no memory of meeting. “I wasn’t asleep,” she said. “It’s sort of like your mind coming back online after it’s been kicked offline. I came out of this blackout on top of a guy I didn’t know, and had no idea how I met,” she said. “It was the weirdest thing that ever happened to me.” She stopped drinking six years ago.

White said this is a common response. Women, he said, are more likely to reduce their drinking because of them, while men often “blow them off.”

While researchers haven’t conducted a large-scale study of the prevalence of blackouts in the general population, White, said, his own research among college students finds that they occur frequently. In 2002, White conducted a study of nearly 800 students at Duke University who had drunk alcohol at some point in their lives. Fifty-one percent said they’d had at least one alcohol-induced blackout. Another study he conducted of incoming college freshman found that among those who’d drunk booze in the previous two weeks, about 12 percent of women and 12 percent of men said they’d blacked out. Many had gotten behind the wheel, had sex, or had engaged in other risky behaviors during their blackouts. Not surprisingly, blackout drinkers are more likely to sustain alcohol-related injuries.

Dr. Carrie Wilkens, a psychologist who is co-founder of the Centers for Motivation and Change in Manhattan, said that sometimes even the spouses of people who have frequent blackouts have no idea they’re in them. Among couples she’s counseled, one spouse might have perfect recall of a vicious argument, while the drinker has no memory of it. “One person is very defensive and confused, while the other is resentful and hurt,” Wilkens said. “It’s hard to get them to work it through.” Sometimes, she tells one partner: “This may never actually get repaired. They may never be able to say they’re sorry or have as much emotion around it because they don’t have a memory of it.”

It’s important to note that not everyone has to be on the severe end of the spectrum for alcohol-use disorder to have blackouts, White says. Until about 20 years ago, scientists believed that blackouts only happened to those who were, but research indicates that they can happen to even occasional drinkers. (Twin studies involving blackouts indicate that some may have a strong genetic vulnerability, since if one twin experienced them, the other was likely to, too.)

But there is a way to avoid them, White said. “Eat before you drink, pace yourself, make sure you’re hydrated, and limit the amount you drink.” While blackouts can happen to anyone, women are at higher risk because they are smaller, have less water, which disperses alcohol, than men, and are more likely than men to skip meals. They also have different drinking habits, he said: Men are more likely to drink beer, while women are more likely to consume wine or spirits, both of which have higher concentration of alcohol than beer.

“Girl on the Train,” likes Rachel’s trips to New York, ultimately leads nowhere good. But it does offer a disturbing image of the blacked-out brain. And it’s nowhere you want to go willingly.