New research shows cannabis harms the lungs in a different way to tobacco.
A study by two New Zealand respiratory specialists found it can cause bronchitis and a destructive disease sometimes known as "bong lung".
"The potential for adverse effects on respiratory health from smoking cannabis has had much less attention than the social and mental health effects," said Professor Bob Hancox, from the University of Otago's department of preventive and social medicine.
Prof Hancox said in statement policies around cannabis use should consider the impact on the lungs.
"Whether liberalising availability will lead to further increases in cannabis use remains to be seen, but it is likely that patterns of cannabis use will change, with resulting health consequences.
"Many people smoke both cannabis and tobacco and are likely to get the worst of both substances."
Although it's difficult to separate the effects of tobacco and cannabis use, Dr Kathryn Gracie of Waikato Hospital's respiratory department said there's "sufficient evidence that cannabis causes respiratory symptoms and has the potential to damage both the airways and the lungs".
"Cannabis may also increase the risk of lung cancer, but there is not enough evidence to be sure of this yet."
The findings were published in the Society for the Study of Addiction journal.
