The "asskicker" coffee has the equivalent of about 52 shots of espresso and comes with a stern health warning.

A small café in Adelaide is brewing something pretty big. The Asskicker ice coffee served at Viscous Café is touted as the strongest in the world, and with a caffeine content over fifty times that of a regular brew, it may well be the case.

To achieve this kind of supernatural strength, the drink's inventor, Steve Benington, tells SBS that he uses a quad espresso over four coffee ice cubes that have been custom brewed for 48 hours. 120 mL of 10-day custom brewed cold drip coffee - or the equivalent of 32 shots - is then added along with four more coffee ice cubes - each equaling a bit over 2 standard shots.

"I use a custom in-house developed brewing method for our cold drip coffee that allows us to brew highly concentrated liquids," he explains.

"All of the caffeine in our drinks is imparted solely via coffee, not via any added substances. Also, the Asskicker contains nothing but coffee so there is no adjusted interactions with sugars or other supplements like there is in standard energy drinks."

The beverage is designed to be sipped slowly over a four hour period and is so potent that it claims to provide drinkers with 12 to 18 hours of caffeinated energy.

Mr Benington explains that it feels "essentially the same as a sustained period adrenaline burst, but not at the full fight/flight level - unless the recommendations are breached."

"Unfortunately the Asskicker tastes really good - more toffee than coffee has been my favourite description given thus far - so trying to make it last the recommended time is part of the challenge of drinking one," he says..

"It is essentially designed to lift you up and keep you there instead of peaking through the roof and dumping you hard later."

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Is that safe?

Each large drink contains an eye-popping 5 grams of caffeine. To put that into perspective, a regular espresso contains between 40 and 90 milligrams of caffeine and a drip coffee between 100 to 150mg.

While there is no conclusive amount of caffeine that’s considered “safe” for consumption, Food Standards Australia and New Zealand state that more than 210mg of caffeine per day has been linked to increased anxiety levels in adults.

The Asskicker therefore comes with a health warning, relevant in particular to people with heart and blood pressure issues and those on certain types of medication.

"The warning is from a practicing GP here in Adelaide and has been confirmed by two southern area paramedics based on their personal consumption of the drink," Mr Benington says.

"I ensure all consumers of the Asskicker are fully aware of the content, recommended consumption times, and early physical signs of having too much too fast.

"We still have to occasionally refuse service if I'm not satisfied that the consumer hasn't taken our recommendations seriously, or they are under 18 essentially".

The drink was originally invented for an emergency worker in need of a serious kick to stay alert. She drank her coffee over two days and stayed awake for three, prompting the beverage to be toned down before commercial sale.