Hallucinogen use has increased since 2015, overall and particularly among adults 26 and older, while use decreased in adolescents aged 12-17 years according to a new study. Estimates of over 5.5 million people in the U.S. used hallucinogens in the past year in 2019, which represents an increase from 1.7 percent of the population ages 12 years and over in 2002 to 2.2 percent in 2019.