(CNN) As freedom to buy and use pot in Colorado has expanded, so has the number of children who've needed medical treatment for accidental exposure to marijuana, a study reports.
The number of Colorado children who've been reported to a poison control center or examined at a hospital for unintentional marijuana exposure annually has spiked since the state legalized recreational cannabis in 2014, according to the study, published this week in JAMA Pediatrics.
Eighty-seven cases of children ages 9 and younger ingesting, inhaling or otherwise exposed to cannabis were called in to the state's regional poison control center from 2014 through 2015 -- more than the 76 total cases in the four years preceding legalization, the study says.
Exposure-related visits for the same age range also rose at Children's Hospital Colorado in Aurora: 32 visits for the first two years after legalization, against 30 visits for the four years prior, according to the study.
Nearly half of the hospital visits since 2009 involved edibles such as brownies and candies. And almost half of the hospital cases in 2014 and 2015 involved recreational, as opposed to medical, marijuana, said the study led by Dr. George Sam Wang, an assistant professor at the University of Colorado in Denver.
Colorado enacted a law last year requiring marijuana products to be sold in resealable, child-resistant packaging. This year, the governor signed a bill banning the production of marijuana treats taking the shape of a human, animal or fruit -- an attempt to prevent people from mistaking them for candy such as gummy bears.
The study's authors say more thought needs to be put into prevention. Wang, in an interview with CNN, noted Colorado's recent prevention laws and said it's possible that the 2015 packaging law curbed the rise in pediatric cases that year.
"I think other states, if they pass laws to legalize marijuana, have to be cognizant of these things and think about" measures to protect children, Wang said Wednesday.
Marijuana ingestion was the most common complaint (74%) in the poison control center calls, the study said.
Symptoms reported in the calls included drowsiness and lethargy (49%), dizziness (12%), agitation (8%), vomiting (5%) and seizures (3%).
Previous studies showed increases in pediatric cases after states decriminalized medical marijuana, as Colorado did in a 2000 vote. This is the authors' first study of pediatric cases in Colorado after the sale of recreational pot was legalized there.
The numbers still are low relative to other kinds of exposure and ingestion cases in this age range. For example, for every 1,000 emergency room visits for ingestion at Children's Hospital Colorado from 2014 through 2015, only 6.4 were related to marijuana, the study said.
"Pharmaceuticals and household products still account for most toddler exposures because they are much more common and available in the household," the study's authors wrote. "However, as marijuana becomes more available, exposures may continue to increase.
"Furthermore, compared with most unintentional pediatric exposures, symptoms after marijuana exposure can be severe: 35% of patients presenting to the hospital required admission, increasing the hospital burden and using more health financial resources."
Colorado is one of three states -- Washington and Oregon being the others -- that have legalized the sale of marijuana for recreational use. People also can legally smoke marijuana recreationally in Alaska and Washington, D.C.
The use of marijuana for medical purposes is legal in 24 states, including Colorado, as well as Washington, D.C.
8 things to know about legal pot
Marijuana still is illegal on the federal level, which means it cannot be transported between states.
The legalization of marijuana for recreational use will be on the ballot on November 8 in five states -- California, Nevada, Arizona, Massachusetts and Maine -- according to the National Organization for the Reform of Marijuana Laws.