Exposure to marijuana in adolescence leads to schizophrenia-like changes in the brain, according to research published in the journal Cerebral Cortex.

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Cannabis, widely used among teens, can have serious consequences.

Statistics from the National Institute on Drug Abuse (NIDA) show that 15% of 8th graders have tried marijuana and over 1% use it daily.

Marijuana, also known as cannabis, can induce sensations of relaxation and euphoria, but anxiety, fear, distrust and panic are also common, especially with high doses or if the marijuana is unexpectedly potent.

Short-term effects include loss of memory and judgment and distortion of perception, leading to impaired performance in school or at work. It can also be addictive.

In teens, marijuana affects brain systems that are still maturing, potentially leading to a negative and long-lasting effect on cognitive development.

Use is related to psychosis

Large doses of marijuana may induce acute psychosis, including hallucinations, delusions and a loss of the sense of personal identity.

Fast facts about marijuana
  • 45% of 12th-grade students in the US have used marijuana at some time
  • 15% have used it within the last month
  • 6% use it daily.

Learn more about marijuana

These reactions are usually unpleasant but temporary; however, longer-lasting psychotic disorders, such as schizophrenia, have been associated with the use of marijuana.

Most of the intoxicating effects that recreational users seek are caused by the main psychoactive - or mind-altering - chemical in the drug, delta-9-tetrahydro-cannabinol (THC).

THC is found in resin mainly produced by the leaves and buds of the female cannabis plant. The plant contains over 500 other chemicals, of which more than 100 are chemically related to THC. Newer strains of cannabis contain higher concentrations of THC.

Researchers from Western University in Ontario, Canada, have shed light on the significant, long-term impacts of THC on the adolescent brain, after exposing adolescent rodents to THC.

The team carried out tests in areas of behavior that are commonly observed in schizophrenia and other neuropsychiatric disorders, such as social interaction, motivation and cognition, exploratory behaviors, levels of anxiety, cognitive disorganization - which is the inability to filter out unnecessary information - and various neuronal and molecular changes.

Using a combination of behavioral and molecular analyses with in vivo neuronal electrophysiology, the team compared the long-term effects of THC exposure in adolescents and adults.

Changes in brain resemble features of schizophrenia

Results showed substantial and persistent behavioral, neuronal and molecular changes that are identical to neuropsychiatric conditions, such as schizophrenia.

Adolescent rodents with THC exposure were socially withdrawn and demonstrated increased anxiety, cognitive disorganization and abnormal levels of dopamine, all of which are features of schizophrenia. These changes continued into early adulthood, well past the initial exposure.

No evidence of harmful, long-term effects was seen in adult rodents, although both adolescents and adults exposed to THC experienced deficits in social cognition and memory.

The behavioral abnormalities seen in adolescents resembled positive and negative schizophrenia-related endophenotypes. A state of neuronal hyperactivity was observed in the mesocorticolimbic dopamine (DA) pathway.

Several prefrontal cortical molecular pathways were also profoundly altered. This is consistent with sub-cortical DAergic dysregulation, a key characteristic of schizophrenia.

The risk profiles for adolescents and adults were different in terms of neuronal, behavioral and molecular markers resembling neuropsychiatric pathology.

With marijuana use widespread among teenagers and the federal government moving toward legalizing it, Steven Laviolette, PhD, who led the research, sees clear implications for the findings.

Laviolette says:

"Adolescence is a critical period of brain development, and the adolescent brain is particularly vulnerable. Health policy makers need to ensure that marijuana, especially marijuana strains with high THC levels, stays out of the hands of teenagers. In contrast, our findings suggest that adult use of marijuana does not pose substantial risk."

First author Justine Renard, PhD, adds that the findings help to explain how adolescent exposure to THC may lead to the onset of schizophrenia in adulthood.

He says: "With the current rise in adolescent cannabis use and the increase in THC content, it is critically important to highlight the risk factors associated with exposure to marijuana, particularly during adolescence."

Medical News Today recently reported that cannabis with high levels of THC can damage brain structures, specifically in the part of the brain that aids communication between the right and left hemispheres.