NEW HAVEN — In the course of 24 hours, New Haven first responders reported nearly 76 overdoses on synthetic marijuana known as ‘spice’ or ‘K2’. So what is synthetic marijuana? It’s been in the news for the past few years. The CDC says that synthetic cannabinoids (cannabis, marijuana) aren’t just one drug specifically. They say hundreds of different synthetic cannabinoid chemicals are made and sold with new ones with unknown health risks becoming available each year.