The adverse health effects and harms related to marijuana use: an overview review

K. Ally Memedovich; Laura E. Dowsett; Eldon Spackman; Tom Noseworthy; Fiona Clement

doi:10.9778/cmajo.20180023

Article Figures & Tables

Figures

Tables

Download figure
Open in new tab
Download powerpoint
Figure 1:
Flow diagram of inclusions and exclusions. CINAHL = Cumulative Index to Nursing and Allied Health Literature.
Download figure
Open in new tab
Download powerpoint
Figure 2:
Summary of evidence. Each dot represents a systematic review. Each third represents the conclusion about harm: the bottom third is no evidence of harm, the middle third is inconsistent evidence and the top third is evidence of harm. Reviews are organized within each third based on quality such that higher quality are near the top of the respective third and lower quality reviews are near the bottom. Some reviews reported on multiple outcomes and are represented accordingly.

Tables

Figures

View popup

Table 1:

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

Area	Outcomes assessed	Reviews included	Primary studies included	Reviews that included randomized studies	Mean quality score^* (range)	Summary of findings
Brain changes	Structural changes Functional changes Chemical changes	15	359	3	4.9 (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
Cancer	Testicular Head and neck Lung Other cancers	4	62	None	7.5 (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	22	394	None	6.4 (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	10	462	1	4.9 (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	5	69	None	5.4 (2–9)	Mother Increased risk of anemia Child 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	12	213	None	3.8 (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).