A study in the December 2018 Pediatrics found that nearly half of hospitalized children in Colorado whose parents enrolled in a smoking cessation program tested positive for marijuana exposure. Authors of the study, “Marijuana and Tobacco Co-Exposure in Hospitalized Children” (published online November 19), said findings suggest prevalent co-use of tobacco and marijuana in the state that could expose children to harmful effects of both. The research involved a secondary analysis of data and samples collected as part of a study to test the effectiveness of a tobacco smoking cessation program offered to parents. All families were recruited after recreational marijuana use became legal in Colorado. Parents in the study reported being current tobacco cigarette smokers, and some also reported using marijuana. Among those who used both there was significantly variability—some primarily used tobacco with occasional marijuana use, while others reported more marijuana and less tobacco use. Testing the participating children’s urine, the researchers discovered that 46% of them had detectable levels of the marijuana metabolite tetrahydrocannabinol carboxylic acid (COOH-THC). In addition, 11% of children had detectable levels of tetrahydrocannabinol (THC), which is used to test for active marijuana use, and suggests a higher level of exposure. While 3 of the 9 study participants who tested positive for THC were adolescents, and potentially marijuana users themselves, 6 of the THC-positive children were ages 7 and under—most with parents who reported marijuana use “some” or “every day.” Study authors said they were not surprised that children with detectable levels of COOH-THC were more likely to have parents who reported smoking marijuana daily in the home, and in a different room if their child was there rather than outside. They pointed out that tobacco smoke and marijuana smoke contain similar harmful chemicals, and smoking in the home—even in a different room—can result in significant exposures to children. Parents and caregivers should be encouraged to avoid smoking tobacco, marijuana, or both in the home, they said, to help reduce exposure to infants and children living there.