Does synthetic marijuana have any negative effects that cannabis does not?

I've done it before, and nothing bad happened, just like how nothing bad happens when I smoke weed. One of the female friends that I was doing it with, however, had a severely negative reaction. She threw up and couldn't walk, her lips lost almost all their color. Afterward she was fine, but I heard the stuff can kill you. Does it kill you if you do too much, or can long term effects build up or what?