Smoking

[iago]

The reason I said "who knows?" is because there are plenty of studies that prove both ways that I've read about.  I don't think we'll ever get a straight answer about it.

Beware of attempts/studies that seek to "prove (something)".  Instead, you should be looking for theories which withstand scrutiny.  Things that cannot be proven false (or have not yet), have more weight with me.  Read about the on-again/off-again theories that the universe exists in "ether" for more discussion on why this approach is preferable.  In math you can prove something right, but I don't think many other areas offer this ability.

Well, in this situation I think it's totally possible to either prove that smoking weed causes permenant damage or that it doesn't, but everybody who tries to go either way has their own agenda and their opinion or study is biased one way or another.