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What Does Marijuana Do to the Brain?

by Crystal Collier, PhD, LPC-S author of The NeuroWhereAbouts Guide and creator of BrainAbouts

How It Works, Naturally

Our brain makes chemicals that send messages throughout our body. These messages tell our brain and body what it needs for survival and health maintenance. Most everyone has heard about one of these chemicals, dopamine, which increases the calm and happy feelings we get after eating, connecting with loved ones, or while using mood altering substances. But not everyone knows about anandamide, dopamine’s less potent cousin.

Anandamide got its name from an old Sanskrit word Ananda, which means joy, bliss, and delight. True to this meaning, anandamide plays a role in regulating eating and sleeping patterns and in pain relief. This chemical binds to receptor sites in the human body’s endocannabinoid system, a system that is involved in regulating a long list of processes including pleasure, memory, thinking, concentration, movement, coordination, and sensory and time perception. 

Anandamide’s job is to help make sure all these systems are working well and staying in balance. Then, along came tetrahydrocannabinol or THC for short. THC is a compound that looks almost exactly like anandamide and because THC’s molecular structure is almost identical, it binds to the same cannabinoid receptors normally occupied by anandamide. 

Hijacked by the Imposter

The endocannabinoid system oversees pain relief in addition to regulating appetite, mood, and memory. When the psychoactive chemical found in marijuana, THC (tetrahydrocannabinol), binds to the receptor sites in the endocannabinoid system, a more intense effect is produced than the one from the body’s natural pain-regulating chemical, anandamide. One might think a more intense relief of pain is a good thing. In fact, there are legitimate pain and inflammation reduction uses for cannabis and other compounds like THC’s non-psychoactive sister, CBD (cannabidiol). However, anandamide’s imposter, THC, poses problems. It can overload the endocannabinoid system interfering with the body’s natural ability to regulate and relive pain. Ironically, this may result in increased pain, sleep problems, depression, or anxiety; the very impetus for use in the first place.

Moreover, THC is psychoactive which means it changes a person’s mental state and the way the nervous system works which can lead to intoxication, tolerance, withdrawals, and dependence. THC compounds are also neurotoxic to brain development by way of shutting down the front lobe while it is growing. And because THC loves to accumulate in fat, it gets stored there for long periods of time potentially arresting neurodevelopment longer than other substances that leave the body faster.

Although the user may prefer the euphoria that occurs when anandamide is bumped out and replaced by THC, the more intense effect from this imposter wreaks havoc on endocannabinoid systems, including appetite, mood, motor function, and memory. These effects may cause cannabis toxicity, hyperemesis syndrome (severe nausea and vomiting), or psychosis. Eventually, the user’s brain may produce less anandamide as the body begins to prefer or become dependent on the imposter THC resulting in cannabis use disorder. See the definitions below for more information.

Critical Lesson: Negative Effects are Greater in Youth

The lists below contain the results of longitudinal research conducted over the past 30 years revealing the harmful physical and psychosocial effects marijuana can have, especially on youth. Marijuana or other cannabis product use is associated with brain structure size differences and alterations in neurodevelopment. There is also executive function impairment in multiple areas, including: 

  • Processing speed
  • Attention
  • Memory
  • Learning
  • Impulse control
  • Decision-making
  • IQ
  • Visuospatial skills

These impairments may sometimes be short-term, but not always. They sometimes persist even after marijuana use is stopped, especially for heavy users. Such longer-lasting problems are less evident in adults who began using cannabis later in life. The good news is that impairments caused by regular use are reversible after sustained abstinence.

Because THC appears to block synaptic plasticity and neurogenesis, the younger the user, the longer development is arrested and the more permanent the damage. Additionally, with marijuana use in adolescence, an increased risk for developing psychosis and clinical depression can persist into adulthood. 

For many adults, occasional marijuana use may be harmless except those who exhibit psychosis, have a toxic reaction, suffer a drugged driving accident, or for the 10-17% who become dependent or addicted. However, for youth under the age of 25, marijuana use has mild to severe negative effects on the developing brain. So, Brain-Savvy Parents have scientific justification for saying ‘No’ to their children about marijuana due to the negative effect on the growing brain. Once kids have grown up and their brains have developed, they can make their own decisions with a fully formed frontal lobe. 

Prevention is key to healthy frontal lobe development. If marijuana use is discovered, seek qualified therapeutic assistance from a professional who works with youth who engage in substance use.

Possible Short- and Long-term Effects

Short-term Use

  • Altered senses, including time
  • Changes in mood
  • Euphoria, excitement
  • Lethargy, catatonia
  • Impaired coordination
  • Sedation, drowsiness
  • Difficulty thinking and problem-solving
  • Impaired memory
  • Impaired ability to learn
  • Altered judgment
  • Agitation
  • Onset of manic symptoms (even if no pre-existing disorder)
  • Increase in anxiety symptoms
  • Suppression of immune system 
  • Worsening of PTSD symptoms
  • Hallucinations, delusions, psychosis
  • Severe anxiety or paranoia

Long-term Use

Brain Health

  • Changed structure, functions, and chemical activity
  • Diminished executive function, attention, learning, memory, and motor skills
  • Diminished visuospatial functioning, verbal learning, short-term memory, and cognitive function
  • Smaller brain regions, such as the hippocampus (memory region)
  • Reduction in expected developmental pruning
  • Cannabis dependence or addiction

Mental Health

  • Altered emotional functioning
  • Depression, anxiety, mania
  • Chronic Psychosis or paranoia
  • Increased risk of schizophrenia
  • Cannabis dependence
  • Lower life satisfaction
  • Overall lower lifetime achievement
  • Negative sexual side effects
  • Exacerbation of emerging or existing mental health issues
  • Lower rates of recovery from mental health problems
  • Increased risk of suicidal risk

Physical Health

  • Sleep problems
  • Testicular cancer
  • Decreased sperm count
  • Chronic bronchitis
  • Lung problems
  • Stroke
  • Drugged driving accidents
  • Negative cardiovascular effects including tachycardia and hypotension
  • Increased developmental and mental disorders in children of mothers who used cannabis when pregnant
  • Abdominal pain, vomiting, or nausea


  • Poor school or work performance
  • Higher risk of dropping out of school/lower academic attainment
  • Potential loss or lower IQ and less crystallized intelligence