The use of marijuana has been linked to the development of many health conditions. But now, researchers say heavy use of the drug could lead to poor memory and abnormal changes in brain function that resemble changes found in schizophrenic individuals.

This is according to a study published in the journal Schizophrenia Bulletin.

Marijuana is a mix of green and brown leaves, flowers, stems and seeds from the hemp plant Cannabis sativa. The leaves contain a mind-altering chemical called delta-9-tetrahydrocannabinol, more commonly known as THC.

According to the National Institute on Drug Abuse, a part of the National Institutes of Health, marijuana is the most common illicit drug used in the US, with young adults having the highest prevalence of use.

The drug can cause a number of short- and long-term effects, but it most commonly affects a person’s heart and mental health.

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Researchers say regular use of marijuana may lead to poor memory and abnormal changes in brain structure similar to changes found in schizophrenic individuals.

With these factors in mind, researchers from the Feinburg School of Medicine at Northwestern University in Illinois, led by Matthew Smith, conducted a study analyzing the brain changes of a group of participants in their early 20s who regularly used marijuana.

All subjects started using the drug around the age of 16 or 17 and had smoked daily for approximately 3 years, although they had been drug-free for 2 years prior to the study. They also had no history of any other drug abuse.

These participants were compared with a group of healthy controls, subjects with a marijuana use disorder, participants with schizophrenia with no history of substance use disorders, and schizophrenia subjects with a marijuana use disorder. There were 97 participants in total.

Results of the study revealed that participants who began using marijuana regularly at the age of 16 or 17 demonstrated deterioration in the thalamus of the brain – an area important for learning, memory and communication.

They also showed abnormal changes in the brain that are linked to working memory – an impairment that commonly leads to poor everyday functioning and academic performance.

The investigators define working memory as the ability to remember and process information “in the moment,” and transfer it to long-term memory if needed.

These subjects also performed badly on memory tasks, and the same abnormal brain structures were apparent 2 years after they stopped using marijuana – indicating long-term effects from heavy use.

Furthermore, the investigators say the deterioration discovered in the thalamus resembles deterioration found in schizophrenic patients who used marijuana.

Of the schizophrenic marijuana users, 90% had been using the drug heavily prior to developing the mental disorder.

The researchers say these findings support previous research suggesting that regular use of the drug may contribute to changes in brain structure associated with having schizophrenia.

Additionally, they note that if a person has a family history of schizophrenia, they could increase their risk of developing the disorder by using marijuana.

Commenting on the findings, co-senior study author John Csernansky, of the Northwestern University Feinburg School of Medicine and Northwestern Memorial Hospital, says:

The abuse of popular street drugs, such as marijuana, may have dangerous implications for young people who are developing or have developed mental disorders.

This paper is among the first to reveal that the use of marijuana may contribute to the changes in brain structure that have been associated with having schizophrenia.”

Northwestern’s Matthew Smith says that although this study provides evidence that marijuana has long-term effects on the brain, even after individuals have stopped using it, further research is needed to fully understand the drug’s effects.

Other studies have detailed positive health effects of marijuana. Medical News Today recently reported on research suggesting that the THC compound in the drug could help treat people with autoimmune disorders.