Regarding lung cancer:
And 88% incorrectly thought tobacco cigarettes were more harmful than cannabis ones - when the risk of lung cancer is actually 20 times higher. [...] smoking one cannabis cigarette increases the chances of developing lung cancer by as much as an entire packet of 20 tobacco cigarettes, the BLF warned.
I thought this was a pretty concerning and eye-opening statistic, since it's both contrary to the evidence I was aware of and would mean smoking marijuana is incredibly dangerous. But when I tried to find their source (a report from the British Lung Foundation) all I saw is the familiar finding that marijuana cigarettes typically contain twenty times the concentration of carcinogenic compounds as tobacco cigarettes, without any evidence that this actually leads to higher cancer rates. And one can readily find large studies explicitly showing no such correlation.
The study also mentions correlations of smoking with acute bronchitis, which seems believable enough -- I'd imagine lighting things on fire and inhaling them is bad for your lungs -- but the info on the BLF website seems to be assuming a consumption rate of 3-4 joints a day, which I imagine (citation?) is well more than the majority of users smoke.
The article does mention at the very end that a marijuana advocate considered the study "misleading, inaccurate and dangerously irresponsible", but to me this hardly redeems the journalist's integrity for claiming the supposed risks of marijuana as fact. Reefer-madness fearmongering is nothing new (and I've seen plenty of pro-herb advocates making just as absurdly unsupported claims in the opposite direction), but I was bothered to see such a dramatic claim presented as fact by the BBC. Thoughts?