Cannabis Science, CBD

Long Term Effects of Marijuana


If you’ve used weed before, you may be well aware of the short-term effects of marijuana. Depending on whether you used a specific cannabinoid product such as cannabidiol (CBD) or you’ve used a product with the full spectrum of cannabinoids, you may experience different effects. Some people feel high and hungry. Others get pain relief, a better night’s sleep, among other effects. However, all of these are characterized as short-term effects. Have you ever wondered about what the long-term effects of weed? Here’s what science says. 

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Long Term Effects of Weed on Mental Health

Many people use weed to treat various forms of mental illness. For example, people who suffer from depression and anxiety have found some relief from their conditions by using weed. Studies indicate that CBD has reduced anxiety while others show THC can reduce stress. In addition to that, people have used weed to get a better night’s sleep. Getting adequate sleep is essential for mental health. 

On the flip side, there can be some negative long-term effects of weed on mental health. Healthline suggests that for people who have schizophrenia “cannabis may make symptoms worse or increase the chances of developing the condition in people who have a genetic predisposition.”

According to Very Well Mind, using weed that is very potent increases your risk of psychosis. The article said, “Chronic smoking of high-potency marijuana has been found to increase the chances of psychosis (by nearly five times) compared to those who have never used the drug.” The risk of developing psychosis is high for those who use marijuana as teenagers or young adults.

Scientific Studies About Weed and Psychosis

There have been scientific studies surrounding psychosis and weed use. According to one study, those who are at ultra-high risk of developing psychosis were found to have high rates of cannabis use and cannabis use disorders. The researchers concluded that interfering with substance use could be beneficial. Another study posited that cannabis use was not the cause but an indicator of a transition to psychosis in those who met the criteria for cannabis abuse or dependence. 

The link between psychosis and weed also appears to be dose-dependent. According to another study, “Current evidence shows that high levels of cannabis use increases the risk of psychotic outcomes and confirms a dose-response relationship between the level of use and the risk for psychosis.” However, there is still doubt on the nature of the relationship because the study concluded that, “…..[A] causal link cannot be unequivocally established”.

Long Term Effects of Weed on Brain

Yes, mental health involves the brain but for this section, we’re looking more at the other ways weed can affect the brain. While we know weed has short-term effects on the brain, the long-term effects need more research. According to a marijuana research report, marijuana can have long-term and even adverse effects on the brain. Weed seems to affect the hippocampus. THC exposure caused structural and functional changes in the hippocampus of adolescent rats according to the report.

The report says that most of the studies were done on rats and that the human studies involve participants who have used other substances. Healthline also said, “In people younger than 25 years, whose brains haven’t yet fully developed, long-term cannabis use can have a lasting detrimental impact on thinking and memory processes.” This isn’t surprising because experts have warned against using weed as an adolescent. 

According to a study, weed use is associated with lower hippocampus volume. The study says, “Lower volume in the right hippocampus in chronic cannabis users was corroborated.”

It also concluded that THC may be the culprit but CBD acts as a protector. The study says, “Higher THC and lower CBD was associated with this volume reduction indicating neurotoxic effects of THC and neuroprotective effects of CBD.”

There is a lot left to research about weed and the long-term effects on the brain. Scientists are still working on finding out the truth. Weed also may be addictive which affects the brain in other ways too. 


Even though the short-term effects of marijuana are well known, the long-term effects are not quite as clear. Science is hinting that marijuana could cause or indicate the onset of mental illnesses. In addition to that, it may have lasting effects on our brains, particularly memory. However, there is still a lot left to learn. Heavy use seems to be the common denominator of all the adverse effects. Maybe avoiding heavy use could prove to be beneficial.


About Trevann

Trevann is Stoner Rotation’s Jamaica-based lead writer for the Science section of our cannabis blog. She graduated with honors receiving her Bachelor of Science degree in Molecular Biology from the University of West Indies, Mona. For the last three years, she has covered some of the biggest questions around cannabis and health underpinned with research from supporting studies, medical journals and scholarly articles. Got something on your mind? You can reach her at [email protected].