Doctors are warning against the use of synthetic marijuana after a recent spike in the number of emergency room visits across the city. 

According to the Health Department, there were more than 120 people treated in the ER during the second week of April alone after smoking synthetic cannabinoids, also as "Spice" or "K2." 

Dr. Howard Forman, of Montefiore Medical Center, says that the drug is a mixture of dangerous chemicals. It can have extreme side effects that require medical attention, including mind-altering hallucinations and even long-term illness. 

The sale and possession of the synthetic substance has been banned in New York since 2012.