Smoke is harmful to lung health. Whether from burning wood, tobacco or marijuana, toxins and carcinogens are released from the combustion of materials. Smoke from marijuana combustion has been shown to contain many of the same toxins, irritants and carcinogens as tobacco smoke.4-7
Links
[1] http://www.lung.org/stop-smoking/about-smoking/health-effects/marijuana-lung-health.html
[2] http://www.rethinkpot.org/tags/lungs
[3] http://www.rethinkpot.org/tags/second-hand-smoke