Sales of caffeinated drinks are booming. But these sugar-packed concoctions aren't always the handy little pick-me-ups they claim to be

Sales of soft drinks have, like most non-essential items, been decreasing since the credit crunched. But it seems our appetite for stimulating energy drinks such as Red Bull, Rockstar and Relentless, is, well, relentless. The energy and sports drink market continues to thrive, with 484 million litres drunk in the UK last year, according to a report by consumer research group Mintel last month.

"Unlike other markets such as smoothies, which were seeing impressive growth until the recession arrived, sports and energy drinks have continued to grow their value," says Jonny Forsyth, senior drinks analyst at Mintel.

Since the mid-Nineties, we've learnt to love the energy drink. We use them to keep us awake at work or at the wheel, and mix them with alcohol on nights out (Vodbull events, where Red Bull is sold with vodka for as little as a pound, are an institution in various university towns). These drinks are often heavily and inventively marketed. With strong brand identities and flashy websites, they make much of their support for cool, creative youth-driven activities, sponsoring sporting events, music festivals and movies. Relentless even features Romantic poetry on its cans – presumably to suggest the mix of caffeine and taurine will recreate a Wordsworthian sense of the "sublime".

Energy drinks are usually carbonated soft drinks, with a mix of ingredients such as caffeine, sugars, vitamins and herbs designed to stimulate the brain and provide extra physical energy. Many include taurine, an organic acid synthetically produced; L-Carnitine, an amino acid derivative which converts fat to energy; plant extracts such as ginseng, gingko and guarana, and carbohydrates such as glucuronolactone. That these drinks might be equivalent to illegal highs is also hinted at in some marketing. This summer Simply Drinks courted controversy with their latest beverage, Simply Cocaine, with its design, featuring a cartoon character named "Charlie", criticised by anti-drugs campaigners. Leicester East MP Keith Vaz got involved last month, asking the Advertising Standards Authority to intervene out of fears that the drink might encourage drug use amongst young people. The makers, meanwhile, defended the name as "a marketing ploy" and "a bit of humour".

Relentless recently launched a "shot" version of its drink, promising to provide the "immediately consumed, big energy hit" that, says brand manager Dave Leslie, "consumers require". It's sold in small, metal-clad bottles that bear more than a passing resemblance to "legal highs".

While concerns that energy drinks might lead to harder stuff seem overblown, the safety of these caffeine-laden products has long been queried in its own right. Energy drinks have become a staple of the long-distance driver, a more refreshing alternative to the double espresso for staying alert behind the wheel. But the Institute of Advanced Motorists (IAM) last month encouraged drivers not to rely on them. Comparing excessive caffeine consumption to drinking alcohol, the independent motoring safety charity warned of the post-energy drink slump, where just over an hour after consuming these products, tired drivers experience lapses in concentration and slower reaction times. Driver drowsiness is a significant danger, accounting for around 300 deaths each year in Britain.

"Energy drinks are good as a quick fix, but no substitute for regular breaks. Having a high-caffeine drink is a one-off hit – you can't repeat it, as this type of drink does not produce the same effect in a couple of hours' time," commented Neil Greig, IAM's director of policy and research.

Energy drinks have also been blamed for problems in schools. Cardinal Newman School in Hove, East Sussex, has asked local shops not to sell them to pupils, after concerns over the impact the high levels of caffeine and sugar were having on students. Their caffeine content means energy drinks are not recommended as safe for children. These drinks are banned due to health fears in countries such as Norway and Denmark.

Anyone who has had one too many cans of Monster or Red Bull can no doubt imagine the horrors that might arise when their sugary caffeine buzz is mixed with teenage hormones. The problem has been rearing its head around the world: four pupils at a school in Florida were admitted to hospital with heart palpitations in 2008, while high-school students in Sydney who suffered dizziness and nausea prompted a government investigation into energy drinks. It concluded that more than three-quarters of the drinks on sale in New South Wales exceeded the state's legal caffeine limits of 320mg per litre.

Red Bull hits this limit, which works out at 80mg per 250ml can; the same as a cup of coffee, according to manufacturers. Many energy drinks have marketed themselves as being larger than Red Bull, with Relentless's 500ml cans and Rockstar even producing a 720ml can that contains three servings: 240mg of caffeine likely to be consumed in one sitting. Rockstar's tiny "shots" pack 200mg caffeine, two and a half cups of coffee's worth, into a 75ml bottle easily downed in one.

The New York Times reported last year on research published by The Journal of American College Health which found links – possibly coincidental – between energy drinks and risky behaviour. Its author, Kathleen Miller, an addiction researcher at the University of Buffalo, suggested that high consumption of energy drinks is associated with "toxic jock" behaviour: risky, aggressive actions including unprotected sex, substance abuse and violence. According to Dr Miller a taste for the caffeinated stuff might indicate a similar taste for behaving badly: "It appears the kids who are heavily into drinking energy drinks are more likely to be the ones inclined toward taking risks."

But the latest trend on the other side of the pond is for anti-energy drinks, which promise to soothe through sipping. Leading the way is Slow Cow (a piece of branding which apparently didn't please Red Bull), a Canadian drink which purports to have canned "an acupuncture session" and "a one-week vacation". Anti-energy drinks' active ingredients are herbs such as chamomile, kava, valerian and lemon balm. Sound familiar? These drinks claim to provide the relaxing sensations the British associate with sitting down for a nice cup of tea. Expect to see them in your local supermarket soon.