The number of people seeking emergency room treatments after consuming energy drinks has doubled in the last four years. NBC News has the story just released from a government survey.

The study estimates the number of ER visits increased from 10,000 to more than 20,000 from 2007 to 2011. The study doesn't say exactly what brought patients to the hospital, but ER doctors have noticed an increase in the number of patients reporting irregular heartbeats, anxiety and even hear attacks after downing an energy drink.

Granted, the 20,000 visits to the ER in 2011 is small in comparison to the 136 million visits in total, but it still raises the question -- are energy drinks really safe?