WASHINGTON, Aug. 4 (UPI) -- Researchers found no link between chronic marijuana smoking as a teenager and the development of depression, psychotic symptoms or asthma later in life, in a study that followed men from their teens to their mid-30s.
"What we found was a little surprising," Dr. Jordan Bechtold, a psychology research fellow at the University of Pittsburgh Medical Center, said in a press release. "There were no differences in any of the mental or physical health outcomes that we measured regardless of the amount or frequency of marijuana used during adolescence."
Previous studies have linked chronic marijuana usage during the teenage years to psychotic symptoms and depression, as well as cancer and asthma. During the 20-year study, Bechtold said researchers found no links to those conditions, or to anxiety, allergies, headaches or high blood pressure.
Researchers followed 408 participants who'd been part of the Pittsburgh Youth Study, which started tracking 14-year-old public school students in Pittsburgh in 1987 to analyze health and social issues. The students were interviewed every year for 12 years, and then again when they were 36. Of the students, 54 percent are black, 42 percent are white, and 4 percent of other ethnicities or races.
When considering data from the study, researchers split the participants into four groups based on their use: 46 percent were low- or non-users, 22 percent were early chronic users, 11 percent only smoked when they were teenagers, and 21 percent started smoking when they were teens and continued to smoke as adults.
Researchers noted that early chronic users peaked at smoking marijuana an average 200 times per year by age 22 and then slowly declining the frequency of their usage.
The researchers said they mounted the study because of increasing concerns about teenage and long-term use of marijuana since it has been made legal in several states in the United States.
"We wanted to help inform the debate about legalization of marijuana, but it's a very complicated issue and one study should not be taken in isolation," Bechtold said.
The study is published in Psychology of Addictive Behaviors.