Under current guidelines, "single occasion risky drinkers" are defined as people who consume five plus standard drinks in one night (or afternoon, now that summer's here).

But what exactly are the risks?

Beyond your standard hangover and texting-the-ex-regret, most of us aren't too clued up on what binge drinking is actually doing to our brain, liver, stomach and heart. And if we did, we probably wouldn't be so blasé about that fifth glass of rosé.

Professor Kate Conigrave, a specialist in addiction medicine at Royal Prince Alfred Hospital, Sydney, and chairwoman of the panel currently reviewing Australia's alcohol guidelines, is well-versed in the short-term effects of overdoing the booze. "Up to 30 per cent of people attending emergency departments have alcohol-related presentations," she says.

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"If I can use a pun, it is sobering." Below, a look at exactly what's going on when you drink too much.

BRAIN DAMAGE

There are reasons some people knock back a "personality drink" before social occasions - alcohol has an immediate effect on the brain, making us feel relaxed and more confident. But the more you drink, the more damaging the impact becomes.

Prof Conigrave cites a study of university students who drank just six drinks once a week (say, Saturday night): "Subtle testing of their memory function detected deficits in their memory," she says.

"People joke that they're ruining a few brain cells when they drink too much, but, for people under 25, the brain is particularly vulnerable."

HEART PROBLEMS

After even a single occasion of heavy drinking, it's not uncommon for people to experience atrial fibrillation - aka holiday heart.

"Alcohol effects the ability of the heart to keep a regular rhythm so even a single occasion of heavy drinking can tip some people over into a fast, irregular rhythm," says Prof Conigrave.

If you're lucky, the condition dies down when you stop drinking, but in some cases, particularly if you have underlying heart problems, it requires hospitalisation.

It's not just the hangover you need to worry about. Photo / 123RF
It's not just the hangover you need to worry about. Photo / 123RF

ALCOHOL POISONING

"Alcohol poisoning is very common, particularly in young people," says Prof Conigrave.

"People who have basically overdosed on alcohol are at acute risk of dying because they've suppressed their whole body so much, their breathing has stopped."

Just as dangerous is when the gag reflex is suppressed by alcohol, which puts people at risk of drowning in their own vomit.

CANCER

"There is no doubt that alcohol is a carcinogen," says Prof Conigrave, pointing to emerging evidence that links even low levels of alcohol with various cancers, particularly breast cancer in women and colon cancer in men.

"We've only recently understood that alcohol is a well-proven risk factor for breast cancer - some studies estimate that across the population, up to 20 per cent of the risk of getting breast cancer may be influenced by alcohol. Everything you drink contributes to that risk, whether it's daily or weekly."

LIVER DISEASE

Of all the cumulative effects of alcohol abuse, liver disease is the most talked about. But even short-term drinking can do serious damage.

"If people have a binge that goes on over a number of days, they can go into acute hepatitis," says Prof Conigrave. "Sometimes you see someone who's gone to Bali and really hit it hard for a week, and they come back bright yellow with acute alcoholic hepatitis."

BLOOD SUGAR

Alcohol can make blood sugar levels plummet, leading to shakiness, feelings of weakness, fatigue and on the extreme end of the scale, seizures.

"If people binge drink on any empty stomach then their blood sugar goes down, and if you're diabetic and you've taken insulin then it might go down further," Prof Conigrave cautions.

A HANGOVER

Of course, the most common side effect of too many beers is a hangover, and the nausea, headaches and general feelings of seediness that entails. "One of the reasons you get a hangover is that alcohol breaks down into a nasty compound called acetaldehyde, which gives you those side effects," explains Prof Conigrave.

The other reasons you feel so rubbish comes down to dehydration (alcohol is a diuretic) and an increase of stomach acid and irritation of the stomach lining (cue nausea).