Potential Harms of Cannabis Use
Cannabis use is associated with significant adverse effects including increased risk of cardiovascular events (myocardial infarction and stroke), psychiatric symptoms (psychosis, mood disorders), cognitive impairment, and physical dependence, with risks increasing with higher doses, higher THC concentrations, and longer duration of use. 1
Acute Adverse Effects
Cannabis can cause numerous immediate adverse effects:
- Neurological effects: Vertigo, dizziness, drowsiness, disorientation, confusion 1
- Psychiatric effects: Hallucinations, anxiety, suicidal ideations, psychotic symptoms 1, 2
- Cardiovascular effects:
- Impaired coordination and performance leading to increased risk of motor vehicle crashes, especially fatal collisions 2
- Cannabis hyperemesis syndrome characterized by cyclic vomiting 2
Chronic Adverse Effects
Long-term cannabis use is associated with:
Cardiovascular System
- Dose-dependent increased stroke risk (more than once-weekly use significantly elevates stroke/TIA risk) 1
- Greater incidence of myocardial infarction, especially in those with pre-existing cardiovascular disease 1
Mental Health
- Exacerbation of psychotic disorders in vulnerable individuals 1, 2
- Development of mood disorders including depression and mania 3
- Cannabis use disorder and withdrawal syndrome 2
- Worsened positive psychotic symptoms (OR 5.21), negative psychotic symptoms, and total psychiatric symptoms (OR 7.49) 3
Cognitive Function
- Neurocognitive impairments, particularly with use during adolescence 2, 4
- Impaired cognition in healthy cannabis users 3
Respiratory System
- Respiratory diseases similar to those seen with tobacco smoking 2
Pregnancy and Neonatal Outcomes
- Convincing evidence for increased risk of:
High-Risk Populations
Certain groups are particularly vulnerable to cannabis-related harms:
Adolescents and young adults (15-34 years) 1, 4
- Developmental cannabis exposure linked to later mental health issues
- Altered brain development with long-lasting effects
- Higher risk of developing cannabis use disorder
- Increased risk of adverse neonatal outcomes
- Potential long-term developmental effects on offspring
Individuals with pre-existing mental health conditions 1, 5
- Worsening of psychiatric symptoms
- Increased risk of psychosis in vulnerable individuals
- Potential interference with psychiatric medications
Patients with cardiovascular conditions 1
- Increased risk of adverse cardiovascular events
- Potential for dangerous interactions with cardiovascular medications
Older adults (>65 years) 1
- Greater sensitivity to cognitive and cardiovascular effects
- Increased risk of falls and injuries
Dose-Dependent Risk
The American College of Clinical Oncology emphasizes that the risk of adverse effects increases with 1:
- Higher doses
- Higher THC concentrations
- Longer duration of use
Special Considerations
- Driving safety: Convincing evidence shows increased risk of car crashes (OR 1.27) 3
- Sleep disturbances: Cannabis can alter normal sleep cycles and lead to poor sleep quality 1
- Medication interactions: Cannabis can interact with numerous medications, including duloxetine, cariprazine, and stimulants, potentially increasing adverse effects 1
Clinical Implications
- Screen for cannabis use patterns in patients with cardiovascular risk factors 1
- Screen for cannabis use disorder in patients reporting regular use 1
- Advise patients about the increasing potency of modern cannabis products 1
- Inform patients about potential side effects and withdrawal symptoms 1
- Recommend alternative evidence-based interventions for conditions patients may be self-treating with cannabis 1
The evidence clearly demonstrates that cannabis use carries significant risks across multiple body systems, with particular concern for vulnerable populations and those with pre-existing conditions.