I think the healthiest way to use cannabis is vaporizing hash oil (not with a vaporizator, but just heating it gently enough). Doing so you only inhale the THC-containing resin, nothing else, like smoke from burnt plant material, tars, etc.
"Everything we do, everything we are, rests on our personal power. If we have enough of it, one word uttered to us might be sufficient to change the course of our lives. But if we don't have enough personal power, the most magnificent piece of wisdom can be revealed to us and that revelation won't make a damn bit of difference." Don Juan Matus - Tales of Power