I dont do it, but my friend does, and I worry about her...
what does smoking pot do to you?
of course its bad for your lung, silly. smoking one joint is like smoking 5 cigarettes. and people die from cigs. but is luckily not as addictive because it doesnt contain the same ingreedients such as nicottine.
and pot slowly kills brain cells, can put you in dangerous situations. and makes reaction time slower. and if you smoke it long enough you may suffer a lot of longer term consequences such as emphazeyma, or bronchitis, and so on. so yeah just maybe advise her to stop or get help. but also you must know you cant force someone to do what is best for them. so just try and thats all you can do.
The smoke itself is harsh on your lungs (hot and unfiltered) but what's in it is FAR less harmful to your body than cigarette smoke.
Also, your lungs clean and repair themselves (as soon as you stop smoking).
Tell her to use a water pipe to filter the heat and smoke - it is much easier on her lungs.
Best of all (other than stopping) would be to get a vaporizer, which is the easiest on the lungs of all.