Learn more about the risks and side effects that are associated with medicinal cannabis.

The safety profile of medicinal cannabis is mainly driven by THC. The short-term side effects of medicinal cannabis are usually mild to moderate, and transient. Some more common side effects include dizziness, dry mouth, disorientation, nausea, euphoria, confusion, and drowsiness. 1,2 Serious adverse events are rare. In terms of the long-term risks of THC, there is less evidence, but the available studies suggest a similar profile to the short-term risks. The long-term risks include:

  • cannabis dependence: THC can produce physical and psychological dependence and has the potential for abuse; care should be taken when prescribing medicinal cannabis to patients with a history of addiction. 3,4
  • psychiatric disorders: use of medicinal cannabis may exacerbate depression, mania, and psychosis; physicians should avoid use in patients with a psychiatric history or monitor patients for new or worsening psychiatric symptoms during treatment. 3,4
  • cognitive impairment: use of medicinal cannabis may be associated with cognitive impairment and altered mental state’ physicians should reduce the dose or discontinue use of medicinal cannabis if signs or symptoms of cognitive impairment develop. 1,4,5

This is not a complete list of all potential side effects from medicinal cannabis. In addition, there are also potential risks to the lungs if cannabis is inhaled (e.g., chronic bronchitis), 1,4,5 and potential risks to the skin if cannabis is applied topically (e.g., contact dermatitis).

Tolerance to the main side effects of medicinal cannabis could develop. This appears to result mostly from pharmacodynamic rather than pharmacokinetic mechanisms. However, tolerance does not appear to develop with regards to intended effects such as improvement of muscle tone and analgesia. 1,4

Medicinal cannabis is contraindicated in patients with a history of a hypersensitivity reaction to cannabinoids, in patients that are less than 18 years old, patients with severe cardiovascular disease, women that are pregnant or breastfeeding, patients with a personal history of mental disease, and patients with pulmonary disease (for inhaled use). 1,4,6

Exposure to cannabinoids could lead to short-term memory impairment. Frequent use of medicinal cannabis in patients under the age of 18 could result in cognitive problems. 1,4,6

Cannabinoids have been shown to pass the placental barrier in pregnant women and use of cannabis during pregnancy may increase the risk of adverse fetal / neonatal outcomes, including fetal growth restriction, low birth weight, preterm birth, small-for-gestational age, admission to the NICU, and stillbirth. Avoid use of medicinal cannabis in pregnant women. 1,4,6

In published studies, offspring of pregnant rats administered Δ9-THC during and after organogenesis have been reported to exhibit neurotoxicity with adverse effects on brain development, including abnormal neuronal connectivity and impairments in cognitive and motor function. 4

The reported effects of inhaled cannabis transferred to the breastfeeding infant have been inconsistent and insufficient to establish causality. Because of the possible adverse effects from medicinal cannabis on the breastfeeding infant, advise women not to breastfeed during treatment with medicinal cannabis. Medicinal cannabis is contraindicated in pregnant women and women that are breastfeeding. 1,4,6

Several studies have determined that cannabinoids can interact with reproductive hormones in men and women, and that they can lead to a decrease in sperm count, concentration, and motility. Patients should be advised of potential risks if they are trying to get pregnant. 4,7

Elderly patients may be more sensitive to cannabinoids, especially if they have kidney or liver problems. Elderly patients are at increased risk for falls because of their underlying disease state, which may be exacerbated by the CNS effects of somnolence and dizziness associated with medicinal cannabis. These patients should be monitored closely and placed on fall precautions prior to initiating medicinal cannabis. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of falls, decreased hepatic, renal, or cardiac function, increased sensitivity to psychoactive effects, and of concomitant disease or other drug therapy. 4,6

Physicians should consider a lower starting dose in patients with renal or hepatic insufficiency. The administration of medicinal cannabis to patients with moderate to severe hepatic impairment is not recommended. 4,6

The symptoms associated with an intoxication by cannabis may include depression, anxiety, panicking, faints, impaired motor coordination, lethargy, and changes in the cardiac rhythm. In general, these symptoms disappear in a few hours. These adverse effects are generally tolerable in healthy adults and can be usually managed with conservative measures. Treatment should be symptomatic. 4

THC can produce physical and psychological dependence and has the potential for abuse. However, not all patients who use medicinal cannabis will develop dependence. 4,8

Exposure to exogenous cannabinoids can lead to decreased CB1 receptor activity, with notable changes in the temporal lobes, posterior cingulate cortices, and nucleus accumbens. Once exogenous cannabinoids are discontinued abruptly, CB1 receptor activity begins to rebound within 48 hours. This can induce an assortment of withdrawal symptoms, including irritability, trouble sleeping, decreased appetite, cravings, restlessness, and/or various forms of physical discomfort. If a patient uses medicinal cannabis frequently (every day) and for a long period of time (months or years), they may have difficulty stopping it abruptly on their own. It’s recommended to down-titrate the patient’s dose slowly, as it mitigates the occurrence of withdrawal symptoms. Care should be taken when prescribing medicinal cannabis to patients with a history of addiction. 4,8

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