More than 30 people had to be taken to hospital in New York after a mass-overdose of synthetic marijuana, police have said. They collapsed or were barely able to walk in the same neighbourhood of Brooklyn after smoking K2. Witnesses reported seeing victims lying on the pavement, shaking and leaning against trees and fire hydrants. In total 33 people were taken to hospital with non-life-threatening injuries, police said. It was not immediately clear what drugs the victims had ingested, but police said some of the victims had been smoking K2, also known as synthetic marijuana. Dennis Gonzalez, of Bushwick, told WNBC-TV that K2 use in that part of Brooklyn was out of control. Although K2 affects the same area of the brain as marijuana, it contains chemicals made in laboratories and sprayed on to dry leaves. These chemicals are not derived from the marijuana plant, according to the Health Department. K2 can cause extreme anxiety, confusion, paranoia, hallucinations, rapid heart rate, vomiting, fainting, kidney failure and reduced blood supply to the heart.