"It is well known that toxic substances in tobacco smoke can damage DNA and increase the risk of lung and other cancers. Scientists were unsure though whether cannabis smoke would have the same effect. Our research has focused on the toxicity of acetaldehyde, which is present in both tobacco and cannabis," the authors added.

They said that the ability of cannabis smoke to damage DNA has significant human health implications especially as users tend to inhale more deeply than cigarette smokers, which increases respiratory burden.

"The smoking of 3-4 cannabis cigarettes a day is associated with the same degree of damage to bronchial mucus membranes as 20 or more tobacco cigarettes a day," they added.

"These results provide evidence for the DNA damaging potential of cannabis smoke," the researchers conclude, implying that the consumption of cannabis cigarettes may be detrimental to human health with the possibility to initiate cancer development."