So just what are these drinks doing to our body? “Well for a start, they have varying levels of caffeine and sugar,” says Emer Delaney, a dietitian and spokesperson for the British Dietetic Association. “And it depends on the age and size of the person drinking them. Children are more sensitive to the effects, but adults also respond to caffeine differently so the effects can vary hugely from person to person.

“These effects begin from the first sip,” says Dr Stuart Farrimond, author of The Science of Cooking. “Energy drinks contain lots of sugar, sweeteners and diluted acids like citric acid, to give them their appealing citrusy tang. The PH level is approaching the level of lemon juice or vinegar, however, which creates acidic conditions in the mouth that are extremely damaging to teeth.

“The acidity and high caffeine levels then have an irritating effect on the oesophagus, so if you’re prone to stomach ulcers or gastritis – an inflammation of the stomach – it can make it worse.

“Energy drinks don’t linger, quickly pass through and within ten minutes have made their way into the intestines where their sugar is quickly absorbed, leading to elevated blood sugar levels. By twenty minutes levels have reached a maximum and drinkers will feel euphoric, stimulated and alert from the sugar.

“By now all the caffeine will also have been absorbed and you’ll be at peak caffeine levels and your brain will be maximally stimulated. At around 40 minutes your brain will release a chemical called dopamine, which is a ‘reward chemical’ – the type that’s released during smoking, gambling or sex. So around now you’ll be feeling good.

“But by 60 minutes your liver begins treating the caffeine like a poison and tries to eliminate it, which is why these drinks have a diuretic effect which can be dehydrating. And between 90 minutes and two hours later you get what’s termed a sugar crash.”

“This comes just as the caffeine is also beginning to wear off,” says Emer Delaney. “So you’re likely to feel exhausted and irritable and teachers have reported seeing higher levels of anxiety, destructive and attention seeking behaviour, and lower moods among pupils who drink energy drinks.”

Delaney also calls the combination of sugar and caffeine a “potent mix”. One recent study found that drinking sugary, caffeinated drinks is more dangerous than drinking caffeine alone. The study – published in the Journal of the American Heart Association – found that drinking four cans of energy drink leads to abnormal changes in blood pressure and heart rhythm within two hours.

Study author Dr Emily Fletcher, from the US Air Force Medical Centre in California, found the study participants who drank the energy drinks still had elevated blood pressure six hours later and said that ingredients other than caffeine, most likely the high levels of sugar, also had “blood pressure alternating affects”.

Women taking birth control pills also take up to twice as long to process caffeine, so like children they’ll feel the effects of these drinks for longer.

One study published in the International Journal of Health Sciences found that drinking more than 200mg of caffeine from energy drinks can cause caffeine intoxication, with symptoms including anxiety, restlessness, insomnia, muscle twitching and digestive irritation.

“The gut doesn’t like caffeine at all,” says Delaney, “and it particularly doesn’t like it in large doses. So energy drinks can cause digestive problems, like diarrhea and IBS-type symptoms.”

The high sugar content of energy drinks is, according to Delaney, a factor in the rates of type 2 diabetes among young people “increasing in leaps and bounds.” Plus, consistently high blood sugar levels can damage your nerves and blood vessels over time, which can lead to heart disease and kidney problems later on.

“If you drink energy drinks regularly you’ll gain weight, which increases your risk of obesity and type 2 diabetes,” she says. “Again, the mix of the sugar and caffeine is a problem because it makes them highly addictive. So when people begin drinking these drinks, they find it hard to stop. And the huge amounts of sugar and artificial sweeteners they contain increase their appetite and contribute to poor food choices overall.”

“Today’s energy drinks have come far from their origins as a sports aid,” says Dr Farrimond. “They’re not being drunk by people doing sports wishing to improve their game, but rather by people who simply enjoy the taste and the feeling they give.

“As for the claims on the cans about added ginseng or B-vitamins, that’s simply fairy dust marketing. There are far healthier ways to stay hydrated, energised and top up your B vitamins than drinking a cheap, sugary, brightly coloured energy drink.”