i know the nicotine in tobacco paralyzes the cilia in the airway, preventing sweeping out of particles. paralysis will often wear off by morning, which is why smokers cough then.

not sure if this also happens with MJ, but afaik, the tar in weed is much worse than tobacco.

anyhoo, smokers have black, hard, inelastic lungs. when you squeeze the lungs from cadavers of smokers, they don't squeeze easy, and don't bounce back.

good news is, over several years, those black lungs will turn back mostly pink if you quit.