• The report by the City University of New York suggests cannabis may be complicating efforts to limit kids' exposure to second-hand smoke
• The rise comes after years of efforts to curb cigarette smoking around kids

A growing number of American parents are using marijuana when they still have children living at home, according to a new study.

The report suggests cannabis may be complicating efforts to limit kids' exposure to second-hand smoke.

Researchers examined data collected from 169,259 US adults from 2002 to 2015. 

During that time, the proportion of parents with children at home who said they used cannabis at least once in the past month rose from 4.9 percent to 6.8 percent.

Over that same period, the proportion of parents with kids at home who smoked cigarettes declined from 27.6 percent to 20.2 percent, the study also found.

'While cigarette smoking continues to decline among parents with children living at home, use of cannabis is increasing among parents and this may as a result lead to an increase in children's exposure to secondhand cannabis smoke,' said lead study author Renee Goodwin of the Graduate School of Public Health and Health Policy at the City University of New York.

The increase in cannabis use appeared to be 'disproportionately common among cigarette smoking parents,' Goodwin said.

'Therefore we may be seeing an increase in exposure to multiple types of smoke/increased amount of smoke in a growing percentage of households with this increase in cannabis use.'

With some forms of marijuana now legal in about 30 US states, concern is mounting in the medical community that many people may falsely assume the drug is harmless and fail to recognize the potential harms to children who breathe second-hand smoke.

'Exposure to secondhand smoke is associated with an increased risk of asthma and many other health risks for children,' Goodwin said. 

'There have been tremendous public health campaigns aimed at decreasing cigarette use overall and at reducing children's exposure to secondhand smoke from cigarettes, but no clinical or public health effort has been made to educate or inform the public about risks of secondhand cannabis smoke.'