THC. While the issue of cancers is debatable - a recent study in england over a 30 year period on people who used thc on a regular basis has found that they end up with lower iq, s. So if you want to have a low iq - then smoke thc.
Cannabis side effect. A recent study by the british lung foundation found that smoking three cannabis joints a day caused the same damage as 20 cigarettes because people tend to inhale the smoke for longer to gain the maximum "hit". The medical community is still debating whether cannabis use leads to lung cancer - but it's a fact that cannabis contains more carcinogens (cancer-causing agents) than tobacco.