From coffee in Europe to kola nuts in Africa, foods and drinks containing caffeine are the most widely consumed psychoactive substances in the world.
Caffeine is socially accepted as a natural pick-me-up, a stimulant that improves alertness and concentration.
But the new wave of "high energy" drinks with relatively large levels of caffeine is causing concern among parents, health care professionals and government regulators.
Marketed aggressively to young people, the drinks promise a buzz, stimulation, or extra energy and alertness during times of stress.
They usually contain 80mg to 150mg of caffeine, no more than a cup of filter coffee. A cup of brewed tea contains about 60mg and caffeinated soft drinks 20mg to 40mg per glass.
Used on their own, or in moderation, the drinks are harmless, but when mixed with alcohol or consumed in quantity the health risks increase dramatically.
Students are particularly fond of drinks such as Red Bull, Dynamite or Mountain mixed with spirits such as vodka and may consume several in a night.
Carbonated Red Bull prominently displays its taurine (a nonessential amino acid) content and claims the drink "Vitalizes body and mind".
Dynamite, the "energy drink", sells itself with "vitamins, mineral salts and caffeine". Mountain claims it is "caffeinated water with supplemental vitamins" and an "intelligent, refreshing drink".
The questions vexing many people is do these drinks deliver what they promise and are they detrimental to your health?
An Australian professor based at NUI Galway published his answers to these questions in a recent issue of Neuro psychobiology.
Contrary to commonly accepted beliefs, Prof Jack E. James's study claims: "No evidence was found that caffeine improves performance, either in the context of acute or habitual use. On the contrary, performance was found to be significantly impaired when caffeine was withdrawn abruptly following habitual use."
The study, Acute and Chronic Effects of Caffeine on Performance, Mood, Headache and Sleep, differed from most previous research in the area because it examined the effect of caffeine over time and used a schedule of its consumption (including dose level and time) that broadly represented typical consumption by the general population.
"Although participants reported feeling significantly more alert and less tired in response to acute exposure to caffeine, these effects were not accompanied by improved performance."
In fact, withdrawal of caffeine led to impaired performance, increase in headaches and reports of sleeping longer and more soundly.
Prof James is an authority on caffeine and its effects on health and has looked specifically at high energy drinks.
"Certainly the claims are totally out of order in terms of what we know about the effects of caffeine. I think there is a worry if unsubstantiated claims are made in the public domain.
"There are other worries in terms of the promotion of caffeine to children," he said.
Children's long-term health is also a concern. "In other work, we've shown regular use of caffeine shows elevated levels of blood pressure over time. You must take into account that caffeine is consumed by over 80 per cent of the world's population. It's a lifelong habit and is very likely to contribute to cardiovascular disease," Prof James said.
Over the years, various studies have analysed potential links to cancer, genotoxicity, reproduction and development, mineral metabolism especially osteoporosis, and cardiovascular disease. None has found significant links to moderate caffeine use, but excessive use is another story.
In response to consumer concerns, the Food Safety Authority of Ireland has formed a committee to study the health claims of these drinks. Dr Patrick Wall is concerned that the drinks may not deliver what they promise.
"The public tends to confuse high energy drinks with isotonic sports drinks," he said. Isotonic drinks, such as Lucozade or Gato rade, are designed to replace fluids lost through physical exercise.
In contrast, high energy drinks contain water, carbohydrates, taurine, glucurnolactone, caffeine, guarana, inositol and vitamins. Guarana is another source of caffeine and therefore increases levels in the drink.
Despite a very different ingredient mix, high energy products tend to market themselves like isotonic sports drinks. "Undoubtedly, the ingredient in high energy drinks that caused the most concern is caffeine," said Dr Wall.
In 1996, the Government's Food Advisory Board released a study on high energy drinks. Some of the recommendations on Irish policy towards these drinks were:
setting the caffeine level at 320mg to 330mg;
possible use of warning labels;
if guarana is present, the total caffeine content should not exceed the stated caffeine limit.