More than 25 percent of women giving birth who test positive for marijuana also using other drugs

An Arizona study found that 26 percent of mothers or their newborns who tested positive for THC also had drugs such as opiods, amphetamines and cocaine in their systems.

The study, to be presented at the American Academy of Pediatrics National Conference & Exhibition in Washington, DC., looked at mother-newborn pairs who testing positive for THC between 2006 and 2010 at an urban, non-profit teaching hospital that averaged 5,000 births per year. Researchers found that more than a quarter of the time when THC was detected in the mother or baby, so were other illicit drugs--most commonly opioids (12 percent), amphetamines (11 percent) and cocaine (6 percent). The drugs were more likely to be detected in the newborns, whose systems can be slower to clear substances from the body than the mothers'.

Lead author Dr. Edith P. Allen, a clinical associate professor of pediatrics at the University of Arizona, said the study's findings suggest that medical providers should be cautious about recommending breastfeeding to mothers who are marijuana users.

"Although breastfeeding is usually healthier for newborns than formula feeding, nursing while consuming illicit drugs is not recommended," she said.

Even in states where consumption of marijuana is legal, Dr. Allen said, doctors may want to consider screening mothers and newborns since THC use can indicate the use of other drugs that could harm the infant.