Cannabis smoking has not been linked to long term lung pathology such as COPD, emphysema or lung cancer.
Chronic regular cannabis smoking can lead to chronic bronchitis due to increased secretions. However, this rapidly resolves when cannabis use is stopped.
2014 – http://onlinelibrary.wiley.com/doi/10.1111/resp.12298/full
2013 – https://www.ncbi.nlm.nih.gov/pubmed/23802821
