Users expecting synthetic marijuana to give them a mellow buzz similar to the real thing can get a nasty surprise, as the two are very different. Chemicals added to synthetic drugs can make them dangerous and sometimes deadly, more similar to PCP.
Sources: Criminal Justice Coordinating Council; To the Maximus Foundation, D.C. Police,D.C. Fire and EMS Department, Office of National Drug Control Policy | Bonnie Berkowitz, Richard Johnson and Denise Lu/The Washington Post July 18