The Long-Term Effects of using Cannabis – What happens if your teen uses cannabis regularly

There have been 2 studies released recently that have looked at the effects of cannabis use (and for the sake of clarity we use cannabis to mean the THC version of marijuana not the CBD version).  Both studies monitored over 1,000 individuals over 20 years to study any effects of early cannabis use. These studies both found that early and daily use lead to cognitive impairment, worse, was that even if the participants quit chronic use they did not recover completely.

A longitudinal study followed 1,000 New Zealanders tracking from birth to their last assessment when they were about 45-years.  Those in the sample that began using cannabis before age 18 and continued to use regularly throughout adulthood were compared to others in the sample.  Several negative impacts were found, most notably the following:

1.   average IQ decline from childhood to age 45 of 5.5 IQ points (almost an average of a half a standard deviation decline)

2.   significantly smaller hippocampus volume (the brain region linked to memory and learning) 

3.   worse performance on learning, memory and information processing tasks

4.   those who quit their chronic cannabis habit did not show the same level of deficits

The other research  associated early cannabis use with adult functioning. In this study, the authors used data from 1,420 participants in the 25-year Great Smoky Mountains Study to test associations of commonly used definitions of early cannabis use with a broad range of adult psychiatric, substance, and real-world outcomes.  

Whereas all individuals who initiated cannabis use during adolescence showed some poor adult outcomes, those early users who used daily and continuously over time were associated with the most severe negative adult outcomes. Cessation of early use did not fully eliminate later risks but was associated with fewer negative outcomes. 

Again, these studies were not done with the current high potency cannabis that is available today.

Our brains do not fully develop until we are about 25 years old.  More and more research is showing that cannabis use for those in their teens can affect their mental health and long-term brain development.