Lung damage isn't permanent. Brain damage is permanent. Well, that depends.

The dust-collecting hairs on in your lungs called cilia are damaged by smoking. They will heal in time, but will take years. If you contract a disease such as emphysema or chronic bronchitis, you will have this condition for life. Quitting smoking will improve this condition, but it will never completely heal.

Cigarettes are usually more harmful then cigarettes for many reasons. First of all, cigarettes are physically addictive. Who do you know that smokes 10-12 joints a day? Plus, industry tobacco contains a lot of chemicals, including polonium 210 (which is used to grow tobacco), which may be harmful if smoked. There's a lot of propaganda that says smoking one joint is equal to [insert imaginary number here] cigarettes. There's been no scientific research that has concluded that that is the case.

The short answer is, you may have some long-term problems if you smoke heavily every day, but you may not develop these problems if you don't. Switching to a vaporizer and ingesting cannabis rather than smoking it will almost completely remove the chances of developing any conditions, though, so maybe you should put down the joint and open up the butter!

Has anyone ever been reported of developing lung cancer from cannabis? No. Does that mean it can't happen, or that someone is lying? Perhaps, and I'm somewhat inclined to believe that it could happen. Just not to someone who smokes 2 or 3 bowls from a bong a day.

I already exited out of the site, so sorry. All of this can be found at webmd if you're willing to spend the time, though.