Cannabis research using the Dunedin Study has found smoking weed is harmful to lung health.

Prolonged cannabis use led to over-inflated lungs, and even increased the resistance to airflow to a greater extent than tobacco.

That can affect our lungs' core function of getting oxygen into our blood.

Although it's one of the world's most widely used drugs, there has been little research on how it affects the lungs.

Study co-author Professor Bob Hancox of Otago University explains the findings to Māni Dunlop.