Cannabis Science

The long and short-term effects of weed on the brain


There is a lot of information going around about the effects of weed. Naturally, not all the information is true or tells the whole story. The truth is weed does affect the brain but that’s not necessarily a bad thing. The effects of weed on the brain can be either positive or negative. How weed affects us has a lot to do with our own genetic makeup, age, and many other factors. Let’s examine the various effects weed has on the brain. 

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What are the short-term effects of weed on the brain? 

Weed has short-term effects on the brain for most people. One such effect is the coveted high people love. 

According to the National Institute of Drug Abuse, when marijuana is used and gets into the bloodstream, it will eventually get to the brain. Tetrahydrocannabinol (THC), the chemical responsible for the high, acts on the brain through the endocannabinoid receptors which respond to other chemicals as well. The article said, “THC acts on specific brain cell receptors that ordinarily react to natural THC-like chemicals.” 

According to the National Institue of Drug Abuse, the following are some short-term effects that weed may cause:

  • altered senses and sense of time 
  • changes in mood
  • impaired body movement
  • difficulty with thinking and problem-solving
  • impaired memory
  • hallucinations (when taken in high doses)
  • delusions (when taken in high doses)

Web MD echoed a similar set of effects but added that your inhibition may be lowered and you could engage in risky behavior. However, the article noted the effects may be dependent on the potency of the weed, how much you took, and how often you use it. 

Other short-term effects of weed on the brain

According to Web MD, marijuana could impair your brain for 24 hours or longer after using it. The article said, “Marijuana can make it harder for you to focus, learn, and remember things.” 

Not all the short-term effects of weed on the brain are negative. People have been using weed to manage their various mental issues. For example, people use weed to manage their OCD symptoms, migraines and Post Traumatic Stress Disorder (PTSD).  Some people have even gotten some short-term relief from anxiety and depression from using weed. 

What are the long-term effects of weed on the brain?

There are a number of long-term effects of weed according to several sources. We’re defining long-term effects as effects that stay with you a while after you’ve used it. 

Addiction or Cannabis Use Addiction

According to Web MD, 1 in 10 people who use weed become addicted. In addition to that, the risk is even worse if you’re using weed as a teen. The article said, “the risk is greater the younger you start marijuana and the more heavily you use it. For instance, the odds of addiction are 1 in 6 if you use pot in your teens. It might be as high as 1 in 2 among those who use it every day.” 

It should be noted that weed isn’t very addictive and Cannabis Use Disorder (CUD) only occurs affects 1.5% of the US population.

In case you’re wondering, addiction has a lot to do with the brain. Addiction Center says that addiction happens when the brain starts the crave the reward of the particular substance. The article continued by saying, “drugs interact with the limbic system in the brain to release strong feel-good emotions, affecting the individual’s body and mind. Our brains reward us when we do something that brings us pleasure.”

Symptoms of Cannabis Use Disorder

According to Stats Pearls, the following are some of the symptoms associated with cannabis use disorder:

  • Inability to fulfill role obligations at work, school, or home as a result of recurrent cannabis use   
  • Cannabis use continues despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by cannabis
  • Considerable time is spent in activities necessary to obtain cannabis, use cannabis, or recover from its effects       
  • Unsuccessful attempts to stop using weed

Mental Illness

While some people are able to use cannabis for the management of their mental illness symptoms, some people aren’t so lucky. According to Web MD, weed may make some people’s mental illnesses get worse. The article said that “using pot may raise your chances for clinical depression or worsen the symptoms of any mental disorders you already have. Scientists aren’t yet sure exactly why”. 

The National Institute of Drug Abuse also echoed similar sentiments. The website noted that long-term marijuana use can cause temporary, paranoia and worsening of schizophrenia symptoms. 

Cannabis Use in Adolescents and Brain Structure

Weed has been linked to negative long-term effects on the brain of adolescents. First of all, using weed as an adolescent is linked to a higher risk of Cannabis Use Disorder (CUD) and addiction. According to the National Institute of Drug Abuse, “people who begin using marijuana before age 18 are four to seven times more likely than adults to develop a marijuana use disorder”. 

 While one study says there are no structural differences as a result of weed use as an adolescent, other studies beg to differ. Other studies showed evidence of decreased right medial orbital prefrontal cortex volume, decreased right medial orbital prefrontal cortex volume, and poorer white matter integrity. One study found that teens demonstrated slower processing speed, poorer verbal learning and memory, and sequencing abilities. 

Other effects on the brain 

There is also evidence that adolescents with cannabis use disorder lose IQ points that they don’t get back in adulthood. Interestingly, this was not seen in people who started smoking cannabis in adulthood. 


Weed has several effects on the brain but remember, not all of them are negative. Some of the more positive effects are the high and alleviation of the symptoms of mental illnesses. Based on the studies, the negative effects of weed on the brain were associated with age, potency, genetic makeup, among other factors.


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].