I looked online but all the sites that dealt with this topic were heavily anti-cannabis or considered this a myth. Ill try again later but maybe there's a better approach than this?

Other causes of concern:
Joints can be dipped in PCP and embalming fluid to enhance marijuana??s effects. Joints laced with cocaine are called ??primo?. While these drugs enhance the initial effects, they also dramatically increase the chances for adverse reactions.
http://www.une.edu/studentlife/health4.asp