If you like energy drinks, you may want to rethink drinking them on an empty stomach.

Our eagle-eyed medical specialist Avis Favaro noticed an item in this week’s Canadian Adverse Reaction Newsletter from Health Canada. The newsletter presented the case of an 18-year-old who drank two cans of Red Bull in half an hour during a night of studying, on an empty stomach. The man was in good health and had no history of seizures or head injury.

An hour later, while he was at school, he suffered two grand mal seizures and had to be taken to the emergency room.

Doctors found no drugs in his system. By the time he arrived at hospital he had normal vital signs and a CT scan and EEG of his brain turned up normal. He was given some acetaminophen and sent home the next day. A year later, he hasn’t had another seizure.

The newsletter notes that in Canada, Red Bull Energy Drink is regulated as a natural health product (NHP). A 355-mL can contains, among other ingredients and vitamins: 

• 113.6 mg of caffeine
• 1420 mg of taurine
• 852 mg of glucuronolactone
• 71 mg of inositol 

According to the product label, not more than one can per day should be consumed a day. It is also not recommended for children, pregnant or breastfeeding women, caffeine-sensitive people, and should not be mixed with alcohol.

This isn’t the first time energy drinks have been linked to seizures. Four other cases have been described in medical journals.  All of them involved adults who had never had seizures before and who drank more than the recommended amount. In two of these cases, the energy drinks were drunk on an empty stomach.

Drs. Stanley Jones P. Iyadurai, and Steve S. Chung, both of the Barrow Neurological Institute at St. Joseph’s Hospital and Medical Center in Phoenix presented their research on the four cases to the annual meeting of the American Academy of Neurology back in 2007. They suggested that large amounts of energy drinks could induce seizures in people who are genetically susceptible.

They noted that guarana seed extract contains guaranine, which stimulates the cardiac and central nervous systems. Animal studies have suggested that taurine has both anticonvulsant and epileptogenic properties, although its effect on humans is not fully understood. And excessive caffeine consumption can lead to increased seizure incidence and a lower seizure threshold in humans.

But the researchers also noted that because there have been so few documented cases, it’s not easy to draw conclusions. They suggested the incidents could be related only by coincidence or by “selective retrospective blame, provoked by questioning."

Health Canada says it is monitoring the use and reported adverse reactions of energy drinks and will "take appropriate measures to safeguard the health and well-being of Canadians."

To report an adverse reaction to an energy drink, please call: 1-866-234-2345 or send in a report electronically to Health Canada's MedEffect section.