You'll get bad gums but not physical health problems from cannabis use.
That's according to follow-up research from Arizona State University and others on the Dunedin Multidisciplinary Health and Developmental Study, which follows 1037 people born in Dunedin in 1972-1973.
The finding publicised by Duke Today, from Duke University, is being reported widely by international media on Friday.
"We don't want people to think, hey, marijuana can't hurt me, because other studies on this same sample of New Zealanders have shown that marijuana use is associated with increased risk of psychotic illness, IQ decline and downward socioeconomic mobility," says Madeline Meier, an assistant professor of psychology at Arizona State University.
"What we're seeing is that cannabis may be harmful in some respects, but possibly not in every way," said study co-author Avshalom Caspi, the Edward M Arnett Professor of psychology and neuroscience at Duke.
"We need to recognise that heavy recreational cannabis use does have some adverse consequences, but overall damage to physical health is not apparent in this study."
Researchers looked at physical health, including lung function, systemic inflammation and several measures of metabolic syndrome, including waist circumference, HDL cholesterol, triglycerides, blood pressure, glucose control and body mass index.
Tobacco users in the study, which appears in JAMA Psychiatry, were found to have gum disease as well as reduced lung function, systemic inflammation and indicators of poorer metabolic health.
"We can see the physical health effects of tobacco smoking in this study, but we don't see similar effects for cannabis smoking," said Ms Meier, who conducted the study with colleagues at Duke University, Kings College in the UK and the University of Otago in New Zealand.
While study participants who had used marijuana to some degree during the last 20 years showed an increase in periodontal disease from age 26 to 38, they did not differ from non-users on any of the other physical health measures.
The decline in periodontal health in pot smokers was not explained by tobacco smoking, alcohol abuse or less tooth brushing and flossing.
The lack of physical health problems among cannabis users also was not attributable to their having had better health to begin with or to living healthier lifestyles.