Cannabis smoke is not as carcinogenic as that of tobacco, according to a research review reported in the Harm Reduction Journal.The two drugs are chemically very similar, but their effects differ due to their respective active ingredients.

Both types of smoke contain the same carcinogenic compounds - but whereas nicotine activates the compounds, THC, the active ingredient in cannabis, has been shown to neutralise some compounds in experiments on mice. The authors warn that, as cannabis is frequently smoked with tobacco, the two together may produce unexpected effects.