Marijuana Effects on the Brain

Marijuana is among the most popular of the recreational and mood-altering drugs on a global basis, and millions of users worldwide are hooked onto it despite the adverse health effects of marijuana on the brain. This is because of the highly addictive nature of this drug, thanks to the intense ‘high’ it produces that attracts the users to try it again and again. However, that does not mean that chronic users can wish away the profound side effects of marijuana on the brain, which can lead to considerable problems such as loss of memory and other cognitive disabilities. Thus, it becomes essential that regular users of marijuana develop a clear understanding of the harms standing in their way both in terms of mental and physical health because of their addiction.

The main majority of marijuana effects on the brain occurs because of the action of its active chemicals such as tetrahydrocannabinoid and other cannabinoid chemicals on the cannabinoid receptors that are present at different parts of the brain. The stimulation of these receptors lead to the release of the chemical dopamine in much higher levels than what is normal. The higher than normal release of this chemical is associated with the healthy pleasurable behaviors such as sex and eating. However, marijuana is able to replicate that pleasurable feeling in the absence of any of the natural triggers of such pleasurable sensations that activate the reward centers of the brain. This results in the initiation of dependence upon the drug for the addicts for getting the same intense feeling of pleasure repeatedly.



Research published in 2005 in the ‘Drug and Alcohol Dependence Journal’ discovered if the constant use of marijuana can affect the brain. The researchers conducted surveys and tests to prove this fact. They conducted Voxel-based morphometry tests to investigate differences in brain tissue composition in 11 heavy marijuana users as well as 8 non-users. They made statistical comparisons to determine differences in gray matter and white matter tissue. The results of the tests show marijuana users have lower gray matter and white matter density as compared to the non–users.

Another study in 2002 published in the ‘Neuropsychopharmacology Journal’ conducted tests on 12 recreational users in a double-blinded placebo-controlled study to determine the effects of marijuana on the brain. They conducted these tests to study the effects of marijuana on the regional cerebral blood flow and cognitive performance among humans. They measured the blood flow before and after smoking. The results conclude that smoking marijuana can cause intoxication but not significantly alter the mean behavioural performance on the attention task. They display increased heart rate and blood pressure.

These studies indicate that heavy marijuana users are shown to have low gray and white matter tissues in the brain. The gray and white matters of the brain are involved in sensory perceptions like speech control, hearing, memory, decision making, self-control, and general function of the brain. So the decrease in these matters explains why marijuana users have a delayed reaction, and don’t seem to be fully conscious and aware of their surroundings after smoking cannabis. However, for basic attention tasks there wasn’t a significant performance difference for users and non-users. This may explain why some marijuana users that are on a ‘high’ are still able to perform basic tasks like writing, reading and observing, without losing too much focus and accuracy.

– Low IQ Levels

Marijuana abuse from the adolescent (teenage) period is often associated with significant decline in the cognitive capabilities of a person later on in their lives. In fact, quantitative tests have shown that the decline in IQ of a person addicted to marijuana during adolescence is as much as eight IQ points. Moreover, these people do not seem to regain their IQ points later on in their adulthood even if they give up on their addiction. However, there is no such loss of IQ points for adults in case of chronic marijuana addiction, but there is some memory impairment. This goes to show the harmful effects of weed on the cognitive development of any person during the formative years.


– Short Term Memory Loss

Chronic addiction to marijuana often leads to a short-term impairment of memory, which can even turn out to be of a much of permanent nature in case of many of the persistent users of this drug. This is because of the structural and functional changes brought about by the active chemical of marijuana, tetrahydrocannabinoid, or THC, that often leads to memory impairment. Thus, the health risks of marijuana include a marked decrease in one’s cognitive functions, and an ability to form new memories. However, the loss of memory is not the only mental problem that is likely to bother any regular user of marijuana, because this drug adds to the risk factor of developing a wide range of psychological conditions.

– Impaired Movement

Marijuana causes considerable damage to the basal ganglia region of the brain, which responsible for the planning of the motor control, as well as, initiation and termination of all movements. Thus, any damage to it is likely to make the addicts severely impaired in terms of their motor controls. This is will make them incapable of driving cars, or handling heavy and sensitive machineries. Thus, addiction to marijuana can entail a considerable amount of damage to the career prospects and self-independence of the addicts. In fact, the harmful effects of weed have a much larger societal perspective in contrary to the common perception, which considers it to be a problem bothering individuals with misconceived thoughts in their minds.


– Schizophrenia, Anxiety & Psychosis

The harmful effects of marijuana on the brain include a marked exacerbation in the symptoms of any preexisting mental conditions such as schizophrenia. In fact, addicts with certain particular types of genetic mutations are much more susceptible towards developing mental illness because of their addiction. In fact, exposure to persistent and high dosage of marijuana during the adolescent period can serve as a causative factor in the development of chronic anxiety and psychosis later on during the adulthood. This psychotic reaction can occur in any user, but it is bound to be much more profound and debilitating in users with preexisting mental conditions such as schizophrenia.

Even in the absence of preexisting mental condition, marijuana users suffer from some of the most common effects of psychotic and mood-altering drugs such as cannabis. The intense ‘high’ produced by this drug may not turn out to be that pleasurable in a significant number of users. In fact, the feeling can be distinctly unpleasant for some of them, with a high level of anxiety and fear marking their ‘high’ period. This feeling of anxiety and paranoia accompanies changes in the vital parameters of health such as heart rate, blood pressure & body temperature. All of these can combine to produce near-fatal and or even fatal consequences. This is particularly true in case of a cannabis overdose, and is a prime cause behind the health risks of marijuana.


– Feeling Un-Motivated

Marijuana effects on the brain can also produce intensely anti-motivational effects for chronic users, because of the growing dependence upon this drug to elicit the feeling of pleasure and reward associated with any accomplishment. Thus, addicts become withdrawn and temperamental in the absence of this drug, and even turn violent to lay their hands on it. Moreover, this drug produces intense ‘high’ feelings, which is difficult to sustain for long, and disappears once the effects of weed wears out. What follows is an extremely vivid period of depression, which can even turn an addict suicidal in the absence of this drug for long. Thus, the marijuana effects on the brain lead to harmful alteration in the behavior of the addicts.

Marijuana addiction is linked with a number of detrimental effects on the health of the chronic users, and the harm it causes to the brain is among the most profound of those effects. The harmful effects of weed are bound to leave its chronic users with an unsound mind and unhealthy body, and especially so in those hooked onto it from an early age.



  • Altered Brain Tissue in Marijuana Users – 2005 – Drug and Alcohol Dependence Journal – by John A. Matochik, Dana A. Eldreth, Jean-Lud Cadet, Karen I. Bolla

  • Effects of Marijuana on the Brain – 2002 – Neuropsychopharmacology Journal – by Daniel S O’Leary Ph.D, Robert I Block Ph.D, Julie A Koeppel BS, Michael Flaum MD, Susan K Schultz MD, Nancy C Andreasen MD, Ph.D, Laura Boles Ponto Ph.D, G Leonard Watkins Ph.D, Richard R Hurtig Ph.D and Richard D Hichwa Ph.D