Marijuana & the Brain: Benefits, Dangers & Signs of Addiction

Marijuana affects the brain in many different ways, impacting the areas of the brain responsible for reaction time, sensory perception, emotions, coordination, decision-making, attention, learning, memory and mood. Notably, using marijuana results in desirable effects like relaxation and euphoria, although unwanted effects like depression, confusion and paranoia can also occur.[1]

Marijuana is thought to be a relatively safe drug; however, it does have some risks when used frequently or in excess. It is especially harmful for children or adolescents. And some people may refer to it as a gateway drug, although that is a controversial subject.

How Does Marijuana Work in the Brain?

The product we call marijuana is a plant with psychoactive properties. Marijuana leaves can be smoked, consumed in edible form, or used topically. There are many active ingredients in marijuana, but two of the most commonly studied are THC and CBD. 

THC acts centrally in the brain, whereas CBD acts more in the body/peripherally and does not have much or any of a psychoactive component. Pure marijuana contains both THC and CBD. However, THC and CBD can be extracted and used separately (you can obtain pure THC without CBD and pure CBD without THC). [8] 

Endocannabinoid System

THC molecules bind to cannabinoid receptors in your brain. Once connected, they disrupt your brain’s communication processes and various physical and mental functions.[1] This network is known as the endocannabinoid system, which plays an essential role in how the nervous system functions, and marijuana use can interfere with various functions, such as:[1]

• Concentration
• Movement
• Cognition
• Memory
• Pleasure
• Coordination
• Time and sensory perception

Marijuana and the Reward System

When someone uses marijuana, THC binds to cannabinoid receptors in the brain’s reward system, causing a surge of dopamine, a chemical associated with feelings of pleasure as well as motivation and memory. This is responsible for the relaxation and euphoria someone feels when they use weed.[1]

Typically, dopamine is released when people engage in pro-survival behaviors like eating and having sex. However, marijuana causes higher levels of dopamine than these natural rewards, which teaches the brain to repeat this behavior. [1]

Marijuana & Your Brain: Short-Term & Long-Term Consequences

Marijuana has both short and long-term consequences of use. 

Short-Term Marijuana Effects

You may only feel the effect of marijuana for a few hours. But researchers can detect changes in brain cells for up to 24 hours.[3] 

Marijuana can impact:[1]

• Attention 
• Coordination
• Memory
• Movement
• Time perception
• Mood

If you are high on marijuana, your judgment and reflexes can be altered. As a result, you should never drive or operate machinery while using marijuana. You are also at increased risks for accidents and self injury. 

Long-Term Marijuana Consequences 

The long term consequences of marijuana use are hard to know and vary depending on each individual’s genetics, use patterns, etc. 

In a study of 4,000 young adults tracked for over 25 years, researchers found that any exposure to marijuana during their lifespan resulted in lower scores of verbal memory.[4] The more marijuana people took, the lower their scores. 

Other research suggests that people who use marijuana regularly have smaller brain grey matter volume than people who don’t use regularly, especially in the parts of the brain controlling:[5]

• Decision-making
• Emotion
• Motivation

Long term consequences of marijuana use tend to be worse if use is started at a younger age: A study of people who started using marijuana in adolescence had an average IQ loss of six to eight points. Those who used heavily as teenagers but quit as adults didn’t recoup the loss. Those who started to use it as adults didn’t have this issue. Therefore marijuana use at a young age may be associated with more serious outcomes than those who begin using as an adult. [4] 

Marijuana Can Negatively Affect Memory

THC changes how the hippocampus and orbitofrontal cortex function. These areas are responsible for forming new memories and shifting focus. [1]

As such, heavy or daily marijuana use can harm your long-term memory and ability to shift attention between tasks.[10]

Heavy Marijuana Use Can Cause Psychosis and Other Psychiatric Disorders

Potent strains of marijuana can cause psychotic episodes in some people. Researchers say smoking strong marijuana every day could increase your chances of psychosis by nearly five times when compared to people who never use.[6]

Repeated use can also increase your risk of mental health disorders, such as:[6]

• Anxiety
• Depression
• Substance use disorders

Research continues to clarify the link between marijuana use and poor mental health [7].

Does Marijuana Have Any Health Benefits? 

Many states authorize marijuana products for medical use for certain medical conditions. For example, there is good evidence that marijuana can help with certain seizure disorders[9,11] 

Marijuana can also be a relatively safe and effective treatment for various chronic pain disorders, and is certainly preferable to prescription opioids in the long-term treatment of chronic pain. Some research has shown that marijuana can help reduce opioid use.[13]

Research also indicates that marijuana and cannabinoids may help treat:[13]

• Epilepsy
• Nausea and vomiting associated with chemotherapy
• Weight loss and loss of appetite related to HIV/AIDS
• Multiple sclerosis symptoms

Withdrawal From Marijuana 

Most people think of marijuana as not being very physiologically addictive, however it is undeniable that people who use marijuana daily and excessively can have mood changes and anxiety/depressive symptoms upon discontinuing use. 

Withdrawal symptoms from marijuana, however, are less severe than other substances like alcohol, and are never life threatening. 

Signs of Marijuana Addiction

About three marijuana users in 10 will develop a marijuana use disorder.[12] This is defined as using marijuana so frequently or in such high quantities that it impairs daily functioning and/or has negative consequences on a person’s life. 

These are signs of marijuana use disorder:[12]

• Using more than you wanted to
• Trying to quit, but finding that you’re unable to 
• Spending a lot of time finding and using marijuana
• Craving the drug
• Continuing to use it even though it causes you problems in your daily life 
• Prioritizing marijuana use over friends and family 
• Using marijuana in high-risk situations like driving or operating machinery. 

If you’re trying to quit marijuana use and can’t seem to make the resolution stick, ask for help from a treatment team. You’ll get help with any unpleasant withdrawal side effects, and you’ll learn how to minimize or even discontinue use altogether, depending on your goals.