The U.S. should prepare for more outbreaks of illness and possible deaths from designer drugs including synthetic marijuana, according to the new research from the University of Colorado School of Medicine.

The study, published in the New England Journal of Medicine, illustrates a wide range of dangers associated with these increasingly popular drugs.

In the fall of 2013, the Colorado Department of Public Health and Environment learned of an unusually large increase in emergency department visits related to synthetic marijuana use in the Denver metro area. Between Aug. 21 and Sept. 19, 263 people visited area emergency rooms with similar symptoms including altered mental status, irregular heart beat and seizures. Approximately 10 percent were admitted to intensive care breathing with the assistance of a ventilator.

Synthetic marijuana is sometimes labeled as incense, potpourri, or herbal smoking blend. It is sold in gas stations and convenience stores, under a variety of brand names including Black Mamba, K2 and Spice. It is a mixture of dried herbs and spices sprayed with chemicals that, when smoked, create a high that is supposed to be similar to THC, the main active ingredient in marijuana. In reality, these agents can cause much more severe symptoms than traditional marijuana.. The package labels often warn that it is not for human consumption.

"These substances are not benign," said the paper's lead author Andrew Monte, MD, an assistant professor in emergency medicine and medical toxicology at CU School of Medicine. "You can buy designer drugs of abuse at convenience stores and on the internet. People may not realize how dangerous these drugs can be -- up to 1,000 times stronger binding to cannabis receptors when compared to traditional marijuana." In addition, synthetic marijuana has effects on serotonin and other stimulant receptors in the brain which can lead to delirium, seizures and strokes.

"Synthetic marijuana is illegal under DEA law, but companies that make it are a step ahead with new chemicals and packaging on standby all the time." said Monte. He goes on to say there has been a significant increase in the use of synthetic marijuana in the last 5 years.

Determining which substance made people in Colorado ill required significant resources from hospitals, Poison Control, Colorado Department of Public Health and Environment, law enforcement agencies and the Centers for Disease Control.

"Outbreaks like this are likely to keep happening," Monte said. "We need better testing to identify these substances, open communication with public health officials when outbreaks occur and we need to make sure physicians ask patients the right questions about their drug use."