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A study has found that heavy cannabis smoking is a major cause of gum disease.
The investigation, which tracked a group of 1000 people born in Dunedin in 1972-73, found heavy cannabis use was responsible for more than one-third of the new cases of gum disease by age 32.
The study involved researchers from the University of Otago, King's College in London, Duke University and the University of North Carolina in the United States.
Professor Murray Thomson from University of Otago School of Dentistry said toxins in cannabis smoke were detrimental to periodontal health.
"The problem is not the smoke itself - it's what's in the smoke," he said.
"In the mouth, there is a fine balance between tissue destruction and tissue healing and the various toxins in cannabis smoke disrupt that."
Professor Thomson said gum disease was one of the most common diseases of adulthood, and caused problems such as the loss of support for the teeth. There was also emerging evidence it could be a risk factor for heart disease, stroke and pre-term birth.
Heavy cannabis users are those who smoke cannabis 41 times or more per year between the ages of 18 and 32.
The study is the first to have investigated whether smoking anything other than tobacco is detrimental for the gums.
The evidence has been published in the prestigious Journal of the American Medical Association.
