Doctors urge moderation when filling up on caffeine.

In recent months, emergency rooms have seen a sharp increase in cases of caffeine poisoning.

Doctors say it's not the energy drinks themselves that have them concerned, but the number consumed in one day, especially by young people.

Another concern for E.R. doctors is the popularity of mixing energy drinks with alcohol.

They warn mixing the two - a depressant and stimulant - can cause major heart problems.