I've read up on a few things, but what are the real health risks associated with heavy marijuana use?
There's no link to lung cancer in smoking marijuana, nor does it cause brain damage. That said, I don't really think there are any besides maybe a smaller lung capacity.
Short term, if you smoke heavily you arent as sharp and coherent. Long term, no damage. Ive seen scans of the heavy user brain, and a normal one and you can tell the difference immediately - lots of dark spots. But the brain is amazing and as any stoner can tell you, after a few days or weeks of sobriety that 'sharpness' returns. ~few good links NIDA - Research Report Series - Marijuana Abuse Heavy Marijuana Use Doesn't Damage Brain
If your brain is still developing and you are a ~chronic user (every week to multiple times a week user), then you will have negative brain effects in some parts of the brain. Not significant if you are older, but if you toke when you are younger than 18 than there is some permanent change in the brain.
I think that brain damage shit is a myth. How can stimulating cannabanoid receptors with a non-toxic chemical damage your brain? Didn't they prove that wrong in the union or something.