even norml comes right out and says it, although they're also being confusing, and it's kind of maddening.

there have been studies that have suggested that the active ingredients in marijuana - thc & cbd - may have anti-oxidant properties, but the way this is presented pretty much everywhere is grossly misleading.

some of the studies have even gone so far as to suggest that thc might shrink tumours, it is true, but what these studies did is inject the compound directly into the tumour at concentrations that are beyond anything we could imagine. you'd have to condense thousands and thousands of joints worth of thc into a syringe to get these kinds of properties. the amount of thc you get from smoking bud is absolutely clinically useless.

so, these reports say things like "it's true that marijuana smoke has been found to produce pre-cancerous cells...but it also has thc", with the implication that it balances out. but, that is dishonest. marijuana smoke has carcinogens in very, very high concentrations (equivalent or higher than tobacco smoke) and trace amounts of anti-oxidants. they don't balance out.

in very, very high concentrations, nicotine could potentially reverse ageing. but, nobody talks about that when discussing the effects of smoking.

you can wait fifty years for these studies to come back, but unless you've smoked yourself retarded, you know it's going to give you cancer - and there's no use in pretending you don't.

http://norml.org/component/zoo/category/cannabis-smoke-and-cancer-assessing-the-risk