Side Effects of Medical Cannabis: What to Expect

Common Short-Term Side Effects

• Dry mouth (xerostomia) is one of the most frequently reported side effects of cannabis
• Dizziness or lightheadedness, particularly on standing, can occur especially with higher doses
• Fatigue or sedation is common, particularly with CBD-dominant or indica-leaning preparations
• Short-term memory impairment and cognitive effects are associated with higher THC doses

Understanding the side effect profile of medical cannabis is essential for both clinicians and patients. The majority of side effects associated with medical cannabis are dose-dependent, reversible, and manageable with appropriate titration and patient education. Distinguishing between short-term effects that typically resolve with continued use and persistent effects that warrant clinical review is an important skill for managing patients on cannabis therapy.

Psychological and Psychiatric Effects

• Anxiety and dysphoria can occur, particularly with high-THC products in susceptible individuals
• Cannabis can transiently exacerbate anxiety in some patients, particularly at higher doses
• Patients with a personal or family history of psychosis require careful clinical consideration
• THC:CBD ratio influences the psychological side effect profile significantly

The psychological side effect profile of cannabis is one of the most important factors in patient selection. High-THC preparations carry meaningful risks for patients with existing anxiety disorders, psychosis history, or cannabis hypersensitivity. The clinical literature consistently supports a cautious, low-dose, slow-titration approach, particularly in patients new to cannabis or those with relevant psychiatric histories. The prescribing clinician’s role in identifying high-risk individuals before initiating treatment is critical.

Cardiovascular and Respiratory Effects

• Cannabis can cause transient tachycardia (increased heart rate), particularly with THC-containing products
• Patients with significant cardiovascular disease warrant careful clinical assessment before prescribing
• Smoked or vaporised cannabis carries respiratory risks associated with the delivery method
• Oral preparations avoid respiratory delivery-related effects but have different absorption profiles

Cardiovascular effects of cannabis are primarily attributable to THC and are generally well-tolerated in young, healthy individuals. In patients with significant cardiovascular disease, hypertension, or a history of cardiac arrhythmia, the risk-benefit assessment requires particular care. The choice of delivery method also influences the risk profile: oral preparations avoid the respiratory effects of inhalation whilst introducing different pharmacokinetic considerations.

Long-Term Safety Considerations

• Long-term cannabis use has been associated with cannabis use disorder in a minority of users
• Tolerance may develop over time, particularly to the psychoactive effects of THC
• Dependence and withdrawal symptoms are possible with chronic high-dose use
• Regular review of ongoing need and continued monitoring of side effects is clinical best practice

The long-term safety profile of medical cannabis continues to be characterised by accumulating real-world evidence. Whilst the evidence base for long-term benefits in certain conditions is strengthening, clinicians should maintain ongoing vigilance for signs of tolerance, dependence, and any change in the risk-benefit balance over time. Regular structured review, including assessment of continued need and side effect burden, is an integral part of responsible medical cannabis prescribing.