In a new study, scientists have discovered that early marijuana use may result in
abnormal brain function and
lower IQ. To conduct this study, four groups of teenagers were recruited:
- Those with depression who were not marijuana users
- Those with depression who were frequent marijuana users
- Frequent marijuana users without depression
- and healthy individuals who were not marijuana users
Participants were later divided into youth who started using marijuana before the age of 17 and those who began using it later or not at all.
These participants underwent psychiatric, cognitive and IQ testing as well as brain scanning. The study found no evidence that marijuana use improved depressive symptoms; there was no difference in psychiatric symptoms between those with depression who used marijuana and those with depression who did not use marijuana.
In addition, results showed differences in brain function among the four groups in areas of the brain that relate to reward-processing and motor control. The use of marijuana did not correct the brain function deficits of depression, and in some regions made them worse.
Of additional interest, those participants who used marijuana from a young age had highly abnormal brain function in areas related to visuo-spatial processing, memory, self-referential activity and reward processing. The study found that early marijuana use was also associated with lower IQ scores.
Since past research has suggested a genetic role between marijuana use and depression, the same participants were genetically tested as well. They discovered that a certain genetic variation of the gene that produces
Brain Derived Neurotropic Factor (BDNF) was found in greater proportion in youth who used marijuana from an early age. BDNF is involved in brain development and memory, among other processes.
The lead scientist concluded that using marijuana does not correct the brain abnormalities or symptoms of depression and using it from an early age may have an abnormal effect not only on brain function, but also on IQ. In addition, this genetic variation may predispose youth to early marijuana use.
One downfall of this study, however, was the small number of participants (74 individuals). These genetic results are therefore tentative and need to be verified with a larger study with more participants.
Source: http://onlinelibrary.wiley.com/wol1/doi/10.1111/acps.12629/full
