Red Bull hit the market first. It was introduced in Austria in 1987. Now it's the world's top selling energy drink, with sales of 2.5 billion cans a year in 130 countries. Each 250-ml can — at a cost of about $3 — contains 80 mg of caffeine.
Part of the concern is that Red Bull is an energy drink, but it doesn't replenish the body after physical exertion (like sports drinks such as Gatorade).
In fact, because Red Bull has so much caffeine — it can actually dehydrate the drinker. That means if you're physically exerting yourself and drink just a Red Bull, the lack of hydration could strain your heart.
And if you combine energy drinks with alcohol, your risk of dehydration rises.
Health Canada has received four reports of adverse reactions to energy drinks. Each case involved "improper use" of energy drinks, such as mixing them with alcohol or drinking too many of them in a day.
The agency recommends that if you do use energy drinks:
* Drink no more than two cans — or 500 ml — a day.
* Do not mix them with alcohol.
* Drink plenty of water if you have an energy drink before intense physical activity or exercise.
The actual caffeine content of energy drinks may be even higher than what's listed on the label. Some contain ingredients — like guarana — that are loaded with caffeine. But because caffeine was not added as a separate ingredient, the label may not have to say the drink contains caffeine.