Synthetic marijuana is believed to have sickened 221 people in Colorado during an outbreak earlier this year.
A Centers for Disease Control and Prevention report released Thursday is based on a joint investigation with state health officials launched after Colorado hospitals started seeing an increase in emergency room visits by people who had used synthetic pot in late August.
Of 127 cases reported in the Denver area and Colorado Springs, 10 were admitted into intensive care but no deaths were reported. Most were treated and released.
The report says the Colorado health and law enforcement officials are looking into whether one of two new variants of synthetic marijuana contributed to the illnesses. One was linked to a similar outbreak in Georgia in August.
Synthetic marijuana is illegal in Colorado. Four stores identified by those who became sick have been closed.
Explore further: US probes likely synthetic pot outbreak