(CNN) — From 2000 to 2017, the rate of exposures to natural psychoactive substances such as marijuana and hallucinogenic mushrooms increased by nearly 75% in the United States, according to a study published Tuesday in the journal Clinical Toxicology.
The study was led by researchers at Nationwide Children's Hospital in Ohio and analyzed 67,369 calls to Poison Control Centers of people inhaling or ingesting natural psychoactive substances. In 2000, the rate of exposure was 17.6 per 1 million people. In 2017, that rate almost doubled -- to 30.7 exposures per 1 million people.
Marijuana made up 46.9% of the calls to Poison Control. The next two substances most frequently called about were anticholinergic plants (21.1%) and hallucinogenic mushrooms (15.6%).
Individuals 13 years and older were involved in 76.2% of the calls; 13-19 year-olds accounted for 34.8% of calls; adults 19 years and older represented 41.4% of the calls.
According to the study, exposure rates for marijuana jumped 150% in the 17 years studied. In 2000, there were 9.9 incidents involving marijuana per 1 million people. By 2017, the rate of marijuana exposures jumped to 24.7 per 1 million people.
The other psychoactive substances assessed included: hallucinogenic mushrooms; anticholinergic plants such as Jimsonweed and Angel's trumpet; nutmeg; kava kava; and the dietary supplement kratom. The only other substance with an increased exposure rate during the study period was kratom. Rates for all other substances trended downward in the 17 year study period.
"These [substances] are viewed as sort of natural. They've been used for ages. So there's almost an assumption that they are safe," said study author Henry Spiller. Spiller is is the director of the Central Ohio Poison Center at Nationwide Children's Hospital. "We want to let [the public] know you do have to be cautious," he added.
The calls studied included 42 deaths -- 20 of which involved marijuana and eight which involved kratom.
Kratom, the stimulant khat, anticholinergic plants and hallucinogenic mushrooms were the substances most frequently associated with hospitalizations.