Vaporizers heat cannabis to release active cannabinoids, but remain cool enough to avoid the smoke and toxins associated with combustion. Vaporized cannabis should create fewer respiratory symptoms than smoked cannabis.
M. Jamalabdollahi, A. Mirzaeinia, and S. Salari. 2012 14th International Conference on Advanced Communication Technology (ICACT), page 832-836. (February 2012)