(CBS) More and more caffeine abuse victims are showing up in the nation's emergency rooms.

A recently-released report from University of Massachusetts Medical School noted 4,600 caffeine-related calls to the American Association of Poison Control Centers in 2005, the most recent data available. More than half involved people under 19, and 2345 required treatment in a health care facility.

"As (caffeinated) drinks become more and more popular, and caffeinated beverages in general, and as the use of them sort of spills over into younger crowds, we're noticing more calls into poison control centers, and more and more of those people are being recommended to go to their local health care facility to get some at least observation and possibly management and treatment," U-Mass Med School toxicologist Richard Church, one of the study's authors, told Early Show co-anchor Maggie Rodriguez Thursday.

"The vast majority of people who experienced some sort of intoxication from caffeine, it's the mild, mild systems," Church observed. "We're talking about some nausea, headache, heart palpitations. People experience insomnia and anxiety. Also, people can experience some daily headaches.

"But it's sort of further down the line where we get concerned as emergency room physicians and as toxicologists. The nausea can lead to intractable vomiting -- vomiting that just isn't necessarily very well-controlled with routine medications we give in the emergency department. People who have predisposed seizure conditions can be at risk for having seizures. People with predisposed heart conditions can have potentially life-threatening abnormal rhythms in their heart."

How much caffeine is too much?

"That's going to depend on the user," Church replied. "Everyone is going to be a little bit different. Like I said, people with predisposed health conditions absolutely are going to potentially have problems with lower doses than the young, healthy person without any prior medical conditions. There is a little bit of research that shows that up to five-to-ten grams in somebody who is young and healthy, without any medical problems, could be potentially a lethal dose."

And energy drinks are "what we would consider a bigger culprit. It's really marketed toward that (the teen) population, if you're looking at the cans and in the grocery stores and such."

But, experts point out, many foods and beverages contain caffeine.

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