Trimethylxanthine — known in some circles as C8H10N4O2 — is the drug of choice for an overwhelming number of North Americans. Most of us refer to it as plain old caffeine.

As many as 80 per cent of us include it as part of our daily ritual. The rest of us probably have some caffeine at some point — often without realizing it.

It's estimated that every man, woman and child consumes about 70 milligrams of caffeine every day — or about the amount in the average 200-millilitre cup of coffee.

But very few of us buy 200-ml cups of coffee. Order a large at your favourite coffee shop and you're getting about 500 ml and anywhere from 200 to 400 mg of caffeine. Have two servings of that size and you're more than likely taking in far more than Health Canada's maximum recommended daily dose of 400 to 450 mg of caffeine.

Caffeine is the addictive element that makes coffee so appealing — and provides the jolt to smooth the transition from sleep to facing another day at work or school.

But if your daily dose of caffeine is up around 600 mg, you may start to show symptoms of caffeine overdose. They will vary from individual to individual, but could include:

• Restlessness.
• Dizziness.
• Nausea.
• Headache.
• Tense muscles.
• Sleep disturbances.
• Irregular heartbeat.

Get up over 750 mg and the list could grow to include:

• A reaction similar to an anxiety attack, including delirium, drowsiness and ringing ears.
• Diarrhea.
• Vomiting.
• Light flashes.
• Breathing difficulties.
• Convulsions.

You can even suffer a fatal caffeine overdose — but you'd have to consume more than 5,000 mg over a very short period of time. That's the equivalent of 50 200-ml cups of strong coffee.

As Canadians we are taking in more caffeine than we used to. Statistics Canada reports that coffee consumption increased from 96 litres per person in 1990 to 106 litres per person in 2009. Consumption of tea — another popular drink that usually contains caffeine — increased even more, from 42 litres per person in 1990 to just under 80 litres per person in 2009.

It's not just coffee or tea that provide a caffeine jolt. You'll get it from some soft drinks, chocolate, cold medications and energy drinks. A 355-ml can of cola has about 36 mg of caffeine. A 50-gram chocolate bar has about 20 mg.

Once caffeine enters your bloodstream, it takes about 15 minutes for you to start feeling its effects. Caffeine stimulates the brain in the same way that cocaine and heroin do:

• It blocks adenosine reception so you feel alert.
• It injects adrenaline into the system to give you a boost.
• It manipulates dopamine production to make you feel good.

For the short-term, your body loves caffeine. But it's the long-term effects that can be a problem. Once the adrenaline wears off, you face fatigue and depression. To turn that around, your body wants more caffeine.

The half-life of caffeine is about six hours. That means if you have a large cup containing 200 mg of caffeine at three in the afternoon, there will still be 100 mg of caffeine in your system six hours later, as bedtime approaches. You may fall asleep, but you might not get the deep sleep your body needs. You wake up tired. You need that caffeine blast. The circle begins again.

Caffeine and kids

What's worrying health officials even more is the increase of caffeine intake among youth. Teens and young adults have been fuelling a surge in sales of energy drinks. In 2005, more than 500 new energy drinks were introduced worldwide.

Red Bull hit the market first in 1987 and its 250-ml cans — boasting 80 mg of caffeine — quickly became a top seller. But, some health experts expressed concern that Red Bull 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.

In September 2008, researchers with Johns Hopkins University in Baltimore called for the caffeine content of energy drinks to be more prominently labelled, given that some energy beverages contain the equivalent amount of caffeine found in 14 cans of Coca-Cola.

On July 26, 2010, an editorial in the Canadian Medical Association Journal called on the federal government to require more stringent labeling of caffeinated energy drinks. The CMAJ said the drinks pose a potential danger to children. Some U.S. drinks contain caffeine concentrations as high as 500 mg.

"Caffeine-loaded energy drinks have now crossed the line from beverages to drugs delivered as tasty syrups," the editorial said.

A statement issued by Refreshments Canada, the organization representing Canada's beverage industry, noted that energy drinks are not sold as foods but as natural health products in Canada – and "are formulated, labelled and marketed in accordance with Health Canada's Natural Health Products Regulation."

The label on a can of the energy drink Original Rockstar says the beverage is "not recommended for children, pregnant or breast feeding women, caffeine sensitive persons or to be mixed with alcohol." A 500 ml can contains 169 mg of caffeine.

Health Canada 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.