PORTLAND, Maine (NEWS CENTER) -- Doctors are warning people to watch their caffeine intake after a 16-year-old in South Carolina died from consuming too much caffeine, according to the Richland County coroner.

Some high school teachers in Maine said they also see their students consuming large amounts of caffeine. Mike D'Andrea, a health teacher at Deering High School, says it is not an uncommon sight.

"We were running the mile in my health class, and one of my students had a monster drink -- like 20 inches -- and I said, it's just not needed," said D'Andrea. "At this age -- everybody's invincible. It's really about that practice -- what am I trying to put in my body? Why am I putting it in my body, knowing that there's a plan."

Medical toxicologist Tammi Schaeffer, D.O. is the medical director of the Northern New England Poison Center, and said different caffeine sources can affect people differently. The average, healthy adult can consume about 400 milligrams of caffeine and be "safe," according to the FDA, but Schaeffer said that many milligrams can sometimes cause people to feel jittery, anxious, nauseous, or experience an increased heart rate.

"Whether they're young, whether they're old, we know that too much caffeine causes problems and certainly, the younger you are, it should probably be moderated more less and less," said Schaeffer.

Schaeffer said a lethal dose would be closer to 5,000 mg (about 50 to 100 cups of coffee), but stressed that very young people, very old people, or anyone with a pre-existing heart condition must limit the amount of caffeine he or she consumes.