It was another regrettably familiar wake-up for Sarah Hepola. Much of her memory from the previous night was blank. She remembers talking to people at a party, but then after that a shadow drops over her memories.

How did she get there, where was the stamp on her hand from? Who bought the pizza? Who was the man beside her?

“I was like, well that’s weird, I don’t know what happened… I just kind of laughed it off, it just seemed normal to me,” she recalls.

This sort of memory loss happened time and again to Hepola – and from a very early age. It often felt like “a trap door had opened underneath me… I would wake up the next day and I would be in a different place,” she says.

She was experiencing alcohol-fuelled blackouts – a colloquial term with potentially serious consequences. As the word suggests, in this state all memories of the night turn dark after a point. Some drinkers experience less severe, fragmentary blackouts where only pieces of memory are lost.

Hepola’s regular blackouts didn’t ring alarm bells for her at the time. It was only looking back that she realised she had a “messed up” relationship with alcohol, experiences she has written about in a book

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If this type of amnesia after drinking alcohol sounds familiar, that’s because blackouts are surprisingly common: one analysis suggests that over half of university-aged drinkers have experienced some level of blackout when asked about their drinking habits, while a survey of more than 2,000 adolescents recently out of secondary school found that 20% had experienced a blackout in the previous six months.

“Fifteen years ago, the field didn’t accept these were common phenomenon,” says Aaron White of the National Institute on Alcohol Abuse and Alcoholism in the US, who spends most of his career studying blackout drunkenness. “Now we are all aware that [many] people blackout.”

Scientists are now revealing more about why blackouts occur and why it affects some more than others – helping them to better understand and hopefully prevent the many negative consequences.

Until recent studies showed otherwise, for many decades it was believed that only alcoholics reached the state of being blackout drunk. A bizarre series of experiments – which never would be ethically approved today – revealed some startling insights.

In the late 1960s, a researcher called Donald Goodwin recruited alcoholics in hospitals and job centres to identify what happens when a drunken memory disappears.  

When they answered, he told them that the pan had dead mice inside

He found that out of 100 alcoholics, more than 60 experienced regular blackouts, some total and some fragmentary. He also revealed that individuals experiencing a blackout can act in a remarkably coherent manner. For instance, he showed that during intoxication subjects revealed “no impairment” of immediate memory and even were able to perform simple calculations. But 30 minutes later, these events were forgotten.

In follow-up experiments, he plied alcoholics with whiskey (up to 18oz – or half a litre – in four hours) and presented them with situations that were set up to “provide memorable experiences, which sober persons have no difficulty remembering”.

In one he showed participants pornography, then asked detailed questions about what they had seen. In another, with a frying pan in hand, he asked individuals if they were hungry. When they answered, he told them that the pan had dead mice inside. The drunk subjects had forgotten these memories after 30 minutes and could still not recall the events the following day. They could, though, recall these events up to two minutes later, revealing that their short-term memory was working.

Though these experiments were performed with alcoholics, they set the stage for understanding how even non-alcoholics act during a blackout. They remain influential in part because today – for obvious ethical reasons – scientists cannot ply participants with alcohol to induce memory loss. They must largely rely largely on questionnaires of past events instead.

It’s like a temporary gap in the tape

That chunks of memory are completely lost during a blackout goes some way into revealing what is going on in the brain. It’s believed that the hippocampus is momentarily impaired – this is the structure of the brain important for weaving together incoming information to create our memories of everyday events. People with severe damage to this area cannot create new memories.

Alcohol therefore shuts off brain circuits central to making episodic memories (memories of specific times and places), explains White, who has studied the process on a cellular level with rodent brains.

“We think a big part of what’s happening is that alcohol is suppressing the hippocampus, and it’s unable to create this running record of events,” he says. “It’s like a temporary gap in the tape.”

In rats, White showed that there are doses of alcohol where brain cells “still kind of work”, and higher doses where they are completely off – which explains partial blackouts where only fragments are lost. At the same time, two other important brain areas that feed the hippocampus information about what’s happening in the world are also suppressed when we drink alcohol, explains White. These are the frontal lobe, the reasoning area of the brain that we use when we’re paying attention to something, and the amygdala, the area that warns us about danger.

Risk factors

We now also know more about other factors that influence blackouts, such as drinking on an empty stomach or when sleep deprived. Another major risk has to do with how fast alcohol is consumed, as the quicker we gulp the faster our blood alcohol level spikes. A blood alcohol level of between 0.20 to 0.30 percent seems to be able to induce a total blackout, where nothing is remembered. That level could be reached by having 15 or more standard UK drinks over four hours, depending on sex and body weight.

But blood alcohol levels do not explain why only some people lose whole chunks of their memory while others who drink similar amounts don’t. A 2016 study led by Ralph Hingson, also of the National Institute on Alcohol Abuse and Alcoholism, provided some answers.

The frequency with which people reported bingeing and being drunk in the past month played a role, as did whether they smoke and took more than one psychoactive drug,” he says.

Blackouts are more common in people with lower body weights. They’re also more common among university students, who are known to ‘pre-game’ to get “a buzz on before they start to socialise, and that makes your blood alcohol level rise fast”, says Hingson.

Across the board there seems to be inherent brain vulnerabilities, and genetic vulnerabilities, that put a person at risk

Women also experience blackouts more often. They are smaller on average than men and have a higher percentage of body fat, which means their bodies have less water to dilute the alcohol they drink – so their blood alcohol level rises faster. In 2017, Amie Haas of Palo Alto University in California found that women would routinely blackout with three fewer drinks than men. A 2015 study showed that women who consumed only one more drink than their usual amount had a 13% higher chance of blacking out than men.

Aside from the sex differences, there could be a genetic component to who is more likely to blackout. Individuals whose mothers had a history of alcohol problems were found to be more at risk. Another study, this time on more than 1,000 pairs of twins, found that a genetic link accounted for half the blackouts experienced.

The genetic difference seems to play out in the brain, too. One longitudinal study of adolescents aged 12-21, led by Reagan Wetherill of the University of Pennsylvania, showed that certain individuals who later went on to abuse alcohol and experience blackouts, were less able to suppress their actions. This could be seen on brain scans, even before they were drinking alcohol.

“Across the board there seems to be inherent brain vulnerabilities, and genetic vulnerabilities, that put a person at risk,” she says.

Worse, studies on mice suggest that heavy drinking may even lead to additional changes in the brain. Equally worrying is that the same people who are more prone to blackouts – teenagers and university students – are at a physically more vulnerable age. “There’s growing evidence that particularly if you are younger, it’s really quite unsafe for a developing brain,” says Haas. That’s because adolescents are more sensitive to the effects of alcohol compared to adults. One reason for this is that the frontal lobe of the brain is the last to develop, at around 25.

Consent wormhole

Like the risk factors, the consequences of blacking out are not only worse for adolescents, but also for women.

Haas and colleagues showed that women who experienced blackouts were more likely to engage in risky sexual behaviour while in a blackout state, compared to men and to drinkers who didn’t blackout at all. These women also showed more regret the following day. 

You have to rely on a preponderance of evidence to determine whether or not consent was given

Evidence also shows that women with a history of sexual assault are more likely to be re-victimised if they are in an alcohol-induced blackout – compared to binge-drinkers who didn’t blackout. This is because they are risk while they under the influence due to impaired decision making, especially when it comes to assessing potentially dangerous situations, but they are also at risk afterwards because they cannot rely on their memory of what happened.

This means there is a catch-22. Those experiencing blackouts may be more vulnerable to potential perpetrators in the moment. But if they try to press charges after, they also are vulnerable to having their cases dismissed.

That is true even in places with an “affirmative consent” standard, where unless someone has indicated their willingness, it’s assault. “If it’s ‘he said/she said’, you have to rely on a preponderance of evidence to determine whether or not consent was given,” says Wetherill.

One party being blackout complicates that evidence. Take Canada, where affirmative consent is necessary. As a Globe & Mail investigation recently found, the courts tend to want a complainant who is so drunk she probably has blacked out at least partially – but at the same time, a complainant who has blacked out isn’t seen as a reliable source of information about what happened.

It’s tricky because people can blackout and look quite sober

In the US, meanwhile, laws vary by state. Most say that someone who is “mentally incapacitated” cannot give consent. But New York, for example, says mental incapacitation can legally result only from involuntarily being given a drink or drug, not from having chosen to drink.

States that include voluntary drinking, on the other hand, usually include the caveat that the accused must ‘reasonably’ have realised the person was incapacitated. But since people who have blacked out can seem highly functioning, the accused can argue that they didn’t realise.

“It’s tricky because people can blackout and look quite sober,” says White. “You don’t always have to [appear] severely intoxicated to blackout.”

Sarah Hepola has ample experience of this kind of disconnect. She says that, during her blackouts, she could still function, take part in conversations and respond to jokes, in the same way that Goodwin’s subjects could perform calculations. Only those who knew her well could recognise her “glassy-eyed unplugged” look of being in a blackout state. “It was like nobody was home… like I was talking but wasn’t receiving,” she says.

But despite how she may have looked to outsiders, she knows she wasn’t herself. “I definitely think my decisions were impaired,” Hepola says. “I was highly impulsive, wildly unguarded and exhibitionistic, even sexually aggressive at times in ways that didn’t make sense to me the next day… based on what people told me.”

This is why some university policies spell it out more clearly: “An individual may experience a blackout state in which they appear to be giving consent but does not actually have conscious awareness or the ability to consent,” Amherst College warns in its sexual misconduct policy. Similarly Michigan University states: “A person who is intoxicated is legally unable to give consent to sexual activity, meaning that sexual intimacy with someone who is ‘mentally incapacitated’ meets the legal definition of a sexual assault.”

Screening questionnaires about alcohol use now routinely ask about prior blackout experiences

It’s perhaps therefore not surprising that a person who regularly experiences blackouts is also more likely to experience other negative consequences of drinking, from the more mundane (like missing appointments or coming to work late) to the more serious (like having an injury or overdosing from using illegal substances). This makes blackouts a useful marker and predictor of other detrimental behaviour.

For these reasons, questions about alcoholic blackouts are now increasingly being used in screening tools to quickly get at whether someone is a recreational drinker or a problem drinker.

Blackout screening

Mary-Beth Miller, an addiction psychologist at the University of Missouri, found that a simple intervention technique could help blackout drinkers reduce their drinking, a finding she first showed in ex-army veterans and then extended to university drinkers.

The intervention is called “personalised normative feedback”. It is an online questionnaire that asks individuals about their drinking habits, and reports back how much they are drinking compared to others who are similar in age and background. Blackouts, her team found, serve as a “teachable moment after which individuals are more likely to respond to intervention”.

 

Screening questionnaires about alcohol use now routinely ask about prior blackout experiences, which could make it easier to target and find individuals who need help. Simply asking about the amount an individual has drunk was not found to be effective. “If you are screening specifically for blackouts, it makes your screening more specific, instead of trying to intervene with every person who comes into your clinic,” Miller says. 

These interventions are not time-consuming or expensive, making Miller hopeful that she and colleagues can build upon them to develop even more effective interventions. She hopes to encourage a drinking culture where people understand that “you don’t have to get completely wasted to have a good time.”

Some messed-up behaviours get laughed off and normalised

Other researchers hope that asking about previous blackouts will in turn help reduce other types of risky behaviour. “It’s definitely interesting that a blackout is one of the most negative consequences of alcohol, and it might be a canary in the coalmine for more significant problems,” Haas says.

For those who experience regular blackouts, a good first step is to better monitor your own alcohol intake and ask friends around you to do the same. That’s easier said than done. For Hepola, it is only looking back that she could see the warning signs. Even at the time she knew she “didn’t want to be that drunk” – but still couldn’t stop drinking.

 “Some messed-up behaviours get laughed off and normalised and sometimes we get distanced from the emotional and physical damage it [alcohol] causes,” says Hepola.

She has now been sober for eight years and is glad to no longer fall into the black trapdoors of memory loss. It has made her life a lot simpler, she says.  

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Melissa Hogenboom is a senior journalist at BBC Future. You can follow her on twitter or facebook.

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