More visits to the emergency department by teens in Colorado are related to marijuana use than in the past, suggesting an impact of the drug’s legalization that needs closer attention, researchers say.

Between 2005 and 2015, the proportion of ED or urgent care visits by youth ages 13 to 20 for marijuana-related illnesses rose from 1.8 per 1,000 visits to 4.9 per 1,000, the study team reports in Journal of Adolescent Health.

“Most studies evaluating the impact of marijuana legalization on adolescents’ use are survey-based studies to evaluate overall recreational use,” said lead author Dr. George Wang, a pediatrician at the University of Colorado Anschutz Medical Campus in Aurora.

And those surveys suggest that teen marijuana use hasn’t increased much in states where the drug is legal, the study team notes.

Marijuana is legal for medical use in 29 states and Washington DC. Eight states plus Washington DC, including Colorado, have legalized recreational use as well.

“We wanted to study the immediate health impact on adolescents, specifically emergency and urgent care visits,” Dr. Wang said in an email. “Marijuana-related (emergency department/urgent care) visits are of significant concern as patients are having significant acute medical or psychiatric symptoms requiring evaluation.”

The researchers analyzed medical records from a children’s hospital system and identified more than 4,000 emergency visits related to marijuana use between 2005 and 2015.

More than two-thirds of the records included information on the patient’s behavioral health and a similar number included a psychiatric diagnosis, such as depression, mood disorder and alcohol abuse, the study found.

Patients had often consumed another substance in addition to marijuana, with alcohol being the most common. About half of the patients were sent home after their emergency visit, 30 percent were admitted to the hospital and the rest were transferred to different facilities.

“Although reports of overall use have not changed, marijuana legalization may impact adolescent and youth in other, potentially more serious, aspects of both their physical and mental health,” Dr. Wang said.

His team continues to stress to pediatricians the importance of screening for substance use and addiction risk factors at an appropriate age, he added. “Furthermore, they should continue to educate families and patients about the potential harms that may result from use at a young age.”

Dr. Sharon Levy, who wasn’t involved in the study, said its results match her clinical experiences in Massachusetts, where laws are also changing.

“We are seeing kids use lots of different products that weren’t available when we opened our program nearly 20 years ago,” said Dr. Levy, who directs the adolescent substance use and addiction program at Boston Children’s Hospital.