Found this

Between the two layers of pleura (the pleural cavity) is a tiny amount of fluid. This acts like lubricating oil between the lungs and the chest wall as they move when you breathe.

Maybe cannabis causes the fluid to dry up?

I have a few friends that have actually quit cause of this stabbing pain

Pleurisy and Pleuritic Pain - Patient UK
lil josh Reviewed by lil josh on . Stabbing pain in lung For about 4 months ive been getting stabbing pains in one of my lungs (usually the left one) when i take a deep breath in but usually only for abgout 2 breaths. Well for the past 2 weeks me and 2 of my mates have been smoking about a quater a day withought fail. Tonight i got the stabbing pain pretty bad but didnt mind as i expected it to go away shortly, however 3 hours later everytime i take a big breath in i get a really sharp stabbing pain :( I dont know what it is or if it has anything Rating: 5