A long-term study of nearly 1,000 New Zealanders from birth to age 38 has found that people who smoked marijuana for up to 20 years have more gum disease, but otherwise do not show worse physical health than non-smokers.

The international research team assessed a dozen measures of 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 online the week of June 1 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 Madeline Meier, an assistant professor of psychology at Arizona State University who conducted the study with colleagues at Duke University, King’s College in the UK and the University of Otago in New Zealand.

While study participants who had used marijuana to some degree over 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. To measure cannabis use, they asked study subjects to self-report their use at ages 18, 21, 26, 32 and 38.

The study’s statistical analysis found that 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.

“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,” Meier said.

“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 recognize that heavy recreational cannabis use does have some adverse consequences, but overall damage to physical health is not apparent in this study.”

“Physicians should certainly explain to their patients that long-term marijuana use can put them at risk for losing some teeth,” said Terrie Moffitt, the Nannerl O. Keohane University Professor of psychology and neuroscience at Duke and co-director of the Dunedin Multidisciplinary Health and Development Study, from which these data were gathered.

This research was supported by the New Zealand Health Research Council, New Zealand MBIE, US National Institute of Aging (R01AG032282, R01AG048895), UK Medical Research Council (MR/K00381X), and ESRC (ES/M010309/1). Additional support was provided by the Jacobs Foundation.

CITATION: “Associations Between Cannabis Use and Physical Health Problems in Early Midlife: A longitudinal comparison of persistent cannabis versus tobacco users,” Madeline H. Meier, Avshalom Caspi, Magdalena Cerdá, Robert J. Hancox, HonaLee Harrington, Renate Houts, Richie Poulton, Sandhya Ramrakha, W. Murray Thomson, Terrie E. Moffitt. JAMA Psychiatry, online June 1, 2016. DOI: 10.1001/jamapsychiatry.2016.0637