Risks of Medical Cannabis
Medical cannabis carries significant risks including neuropsychiatric adverse effects (particularly at higher doses), respiratory harm from smoked forms in patients with lung disease, cannabis use disorder development, and cognitive impairment—risks that must be carefully weighed against potential benefits before prescribing. 1
Key Risk Categories
Neuropsychiatric Adverse Effects
- Acute psychiatric symptoms can occur including panic attacks, psychotic symptoms, anxiety, deficient attention, and impaired concentration, particularly dose-dependent at higher doses 1, 2
- Elevated risk for psychotic disorders in adulthood, especially with early initiation and chronic use 1
- Depression and suicidal ideation are associated with cannabis use, particularly in adolescents 1
- Cannabis use disorder (CUD) affects up to 10% of users who meet criteria for lifetime dependence, with withdrawal symptoms including irritability, insomnia, and headaches 1, 3
Cognitive and Neurodevelopmental Effects
- Adolescent brain development is particularly vulnerable, with evidence showing neuropsychological and neurodevelopmental decline when use begins in youth 1
- Memory impairment occurs acutely and becomes more significant with chronic use, affecting executive function, attention, and processing speed 3
- Neuroimaging studies demonstrate reduced hippocampal volume and density with long-term use 3
- Earlier age of initiation carries higher risk for long-term neurocognitive deficits and development of use disorder 1, 3, 4
Respiratory and Cardiovascular Risks
- Harmful effects of smoked cannabis are particularly concerning in patients with preexisting severe lung disease 1
- Chronic bronchitis may develop with long-term smoked cannabis use 4
- Acute cannabis toxicity in older adults may be associated with sedation, obtundation, and myocardial ischemia or infarction 1
- Tachycardia is a recognized acute adverse effect 5
Special Population Considerations
Pregnancy and breastfeeding: The U.S. Surgeon General and FDA advise complete avoidance of cannabis in any form, including CBD products, due to negative effects on fetal brain development and increased risk for premature birth 1
Older adults (≥65 years): This population faces higher risk for behavioral health issues including anxiety and depression, with increasing cannabis-related emergency department visits 1
Pediatric exposures: Unintentional cannabis exposures in children increased dramatically from 207 cases in 2017 to 3,054 in 2021, causing central nervous system depression, vomiting, and tachycardia 1
Functional Impairment
- Motor vehicle accidents risk increases due to impaired reaction time, coordination, and judgment 1, 4
- Social dysfunction may result at work or school 4
- Motor incoordination and impaired concentration occur acutely 2
Dosing and Administration Risks
- THC total daily dose should generally be limited to 30 mg/day or less to avoid psychoactive sequelae and development of tolerance 5
- Higher THC content in modern cannabis products (due to selective breeding) combined with often undetectable cannabidiol levels increases risk 2
- Dose-dependent effects mean that neuropsychiatric adverse effects are more pronounced at higher doses 1
Risk Mitigation Considerations
Prior cannabis use history: Evidence suggests medical cannabis may be more effective (and potentially better tolerated) in patients with a history of prior cannabis use, though this must be balanced against addiction risk 1
Cannabis use disorder screening: Patients with existing cannabis use disorder face heightened addiction risk and should be carefully evaluated before prescribing 1
Lung disease contraindication: Smoked forms should be avoided entirely in patients with preexisting severe lung disease 1
Evidence Quality Context
The American Society of Clinical Oncology (2016) and HIVMA/IDSA (2017) guidelines both acknowledge that while medical cannabis may provide benefits for refractory chronic pain, the evidence quality is intermediate with moderate strength recommendations, and insufficient evidence exists to recommend it as first-line therapy 1. The American College of Physicians (2024) notes that a 2022 meta-analysis found cannabis products "may be associated with short-term improvements in chronic pain and increased risk for dizziness and sedation" 1.