Table 1:

Summary of findings from 68 systematic reviews on adverse health effects and harms of marijuana use

AreaOutcomes assessedReviews includedPrimary studies includedReviews that included randomized studiesMean quality score* (range)Summary of findings
Brain changes
  • Structural changes

  • Functional changes

  • Chemical changes

1535934.9 (1–8)Association
  • Amygdala, hippocampal, white and grey matter volume, blood flow

  • Learning, attention, memory, overall activity

  • Glutamate, dopamine, N-acetylaspartate, myo-inositol, choline GABA

No association
  • Intracranial and whole brain volume, corpus callosum

  • Testicular

  • Head and neck

  • Lung

  • Other cancers

462None7.5 (5–9)Association
  • Testicular cancer

No association
  • Head and neck, lung or other cancers

Mental health
  • Psychosis and schizophrenia

  • Anxiety

  • Suicide and depression

  • Mania

  • Neurologic soft signs

22394None6.4 (1–10)Association
  • Psychosis, earlier onset of psychosis, relapse and readmission to hospital

  • Death by suicide, suicidal ideation, suicide attempt, depression, more severe mania, anxiety

No association
  • Neurologic soft signs

Neurocognitive effects
  • Learning and memory

  • Executive function

  • Motor function

  • Reaction time

  • Attention

  • Forgetting/retrieval

  • Anhedonia

  • Sleep

1046214.9 (3–9)Association
  • Functional and structural integrity, memory and learning, anhedonia

Inconsistent evidence
  • Learning, attention, forgetting/retrieval, executive function, motor and perceptual motor function, sleep

No association
  • Reaction time, verbal/language skills, visual spatial ability

In those with psychosis
  • No changes to cognitive ability and intelligence, attention, executive abilities, working and learning memory, retrieval and cognition, learning abilities, visuospatial abilities

Prenatal exposure
  • Harms to the mother

  • Harms to the child

569None5.4 (2–9)Mother
  • Increased risk of anemia

  • Decreased birthweight

  • Increased NICU use

  • Effects in later life

Overall health effects and harms
  • Stroke

  • Atrial fibrillation

  • Bronchodilation

  • Respiratory complication

  • Interactions with other drugs

  • Vision

  • Arteritis

  • Risk of a motor vehicle collision

  • Overall mortality

12213None3.8 (2–8)Association
  • Stroke, atrial fibrillation, bronchodilation, respiratory outcomes, lung bullae, COPD, emphysema, lung hyperinflation, infectious disease transmission, interactions with drugs, residual effects on vision

  • Fatal motor vehicle collisions

No association
  • Arteritis, overall mortality

  • Note: COPD = chronic obstructive pulmonary disease, GABA = γ-aminobutyric acid, NICU = neonatal intensive care unit.

  • * Quality score out of 11 (0–4 indicates low quality and 9–11 indicates high quality).