Cannabis Causes Brain Damage

Loss of Gray Matter

Recent studies have reported that cannabis and cigarette smoking are associated with MRI findings of diminished brain tissue in psychotic and nonpsychotic people. Rates of cannabis use and smoking are much higher in patients who develop schizophrenia and may contribute to brain volume differences. It was found that cannabis-using patients who were followed for 5 years had greater losses in gray matter volumes and increases in lateral ventricle volumes than patients who were not abusing cannabis.

mental disorder

Alcohol is also known to lead to reduction in brain tissue volumes and to compound the differences observed in patients with schizophrenia. That cannabis, alcohol, and smoking may all contribute to the magnitude of gray matter loss observed in patients with schizophrenia is supported by recent findings by Stone who found that at low to moderate levels, all were associated with lower gray matter volumes in individuals at high risk of psychosis and in healthy people. Together with the effects of antipsychotic medications, these factors appear to account for the majority of the so-called “progressive” brain changes.

Mental Illness

In addition to producing dependence, cannabis use is associated with a wide range of psychiatric disorders. There is a clear relationship between the use of cannabis and psychosis, different hypotheses for the same have been propounded. There is strong evidence that cannabis use may precipitate schizophrenia or exacerbate its symptoms. There is also reasonable evidence that cannabis use worsens the symptoms of psychosis.

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Heavy cannabis (30-50 mg oral and 8-30 mg smoked) use can specifically cause a mania-like psychosis and more generally act as a precipitant for manic relapse in bipolar patients. It is possible that cannabis exposure is a contributing factor that interacts with other known and unknown (genetic and environmental) factors culminating in psychiatric illness. It is noticed that in many developed countries, persons with severe mental disorders are more likely to use, abuse, and become dependent on psychoactive substances especially cannabis as compared to the general population.

In an interesting study from Pakistan, major metabolites of cannabis were found in the milk of cows which had grazed upon naturally growing cannabis vegetation. Children fed on such milk showed metabolites of cannabis in the urine, suggesting passive consumption through milk.

Neuropsychological Decline

In a study of 1,037 individuals followed from birth (1972/1973) to age 38 y. Neuropsychological testing was conducted at age 13 y, before initiation of cannabis use, and again at age 38 y, after a pattern of persistent cannabis use had developed. Adolescent-onset users showed GREATER IQ DECLINE than adult-onset cannabis users. Moreover, cannabis-associated neuropsychological decline is not reversible.

Recently a study was performed to examine the effects of smoked or ingested cannabis on cognitive function in patients with MS. It was found that cannabis users had greater deficits on information processing speed, working memory, executive function, and visuospatial perception compared to a sample of nonusers group-matched on age, sex, education, premorbid intelligence, EDSS, and disease course. About fifty percent of users were classified as cognitively impaired. Cannabis users are significantly more likely to be classified as globally impaired compared to nonusers.


  1. The Myth of Schizophrenia as a Progressive Brain Disease
  2. Chemistry, Metabolism, and Toxicology of Cannabis: Clinical Implications
  3. Persistent cannabis users show neuropsychological decline from childhood to midlife
  4. Cannabis users with multiple sclerosis are globally mentally impaired compared to nonusers



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