Teens and pre-teens may be puffing on cigarettes less, but they are inhaling pot a lot more. Adolescent marijuana use has increased in the last decade and that's not good according to a new study that suggests teens that smoke pot may suffer a considerable decline in IQ that lasts into adulthood.
In a New Zealand study, more than 1,000 adolescents who began smoking marijuana before age 18, showed an 8 point drop in IQ between the ages of 13 and 38. The average IQ is 100 points. A drop of eight points represents a fall from the 50th percentile to the 29th percentile in terms of intelligence.
As a part of the study, IQ tests were performed at age 7,9,11 and 13, most likely before any marijuana use then again at age 38. The decline in IQ was seen only in the participants who began using marijuana regularly before the age of 18.
Family members and close friends were also asked to complete questionnaires about the 38 year-olds. The questions pertained to any trouble they might have noticed about the participant's ability to stay focused, any memory loss or the ability to function socially.
The eight-point drop was noted in the subjects that were habitual users smoking marijuana at least four days per week. People who started smoking in adolescence but smoked less often still had a hit in their IQ's, but it was less pronounced than the group that used it early and persistently.
On the other hand, kids who never smoked marijuana actually gained one IQ point on average.
Madeline Meier, lead researcher and a post-doctoral associate at Duke University, said that persistent use of marijuana in adolescence appeared to blunt intelligence, attention and memory. More persistent marijuana use was associated with greater cognitive decline.
Collectively, these findings are consistent with speculation that cannabis use in adolescence, when the brain is undergoing critical development, may have neurotoxic effects, Meier writes in the study.
Adverse effects and some neurological effects persisted into adulthood for the children who smoked pot on a regular basis before the age of 18.
Why does marijuana use effect adolescents more than adults? Experts in child development said the reasons could have to do with a substance called myelin. Myelin can be thought of as a kind of insulation for nerve cells in the brain that also helps speed brain signals along and in adolescent brains, the protective coating it forms is not yet complete.
Frontal lobe myelination is not fully completed until age 25 years or so, and the pre-myelinated brain is more susceptible to damage from neurotoxins, says Dr. Richard Wahl, director of adolescent Medicine at the University of Arizona. Cannabis, most likely, is a neurotoxin in high and continuous doses.
One of the major difficulties in getting the message across to teens that smoking pot can be detrimental to their long-term health is their attitude. Many teens believe that smoking cannabis may be illegal, but it's not dangerous.
Increasing efforts should be directed toward delaying the onset of cannabis use by young people, writes Meier, particularly given the recent trend of younger ages of cannabis-use initiation in the United States and evidence that fewer adolescents believe that cannabis use is associated with serious health risk.
The findings provide evidence for the actual rather than ideological and legal basis for concerns regarding cannabis use, said Dessa Bergen-Cico, a assistant professor of public health, food studies and nutrition at Syracuse University. These findings reinforce recommendations on the importance of primary prevention, evidence based drug education and policy efforts targeting not only adolescents, but elementary age children before they start.