The increasing use of cannabis, both recreationally and medically, adds complexity to medical procedures requiring anesthesia. Anesthesia involves the controlled, temporary loss of sensation or awareness achieved through precise drug management. For cannabis users, the interaction between cannabinoids and anesthetic agents can alter how the body responds to standard medication doses. Understanding these pharmacological interactions is important for patient safety and effective management during surgery.
How Cannabis Interacts with Anesthetic Agents
Cannabinoids like tetrahydrocannabinol (THC) and cannabidiol (CBD) engage with the body’s endocannabinoid system, which regulates pain, mood, and nerve function. Chronic cannabis use often leads to tolerance within the central nervous system, making the patient less sensitive to the sedating effects of certain drugs. This pharmacological tolerance directly impacts the effectiveness of common anesthetic and sedative medications, such as propofol and midazolam.
The metabolism of both cannabinoids and many anesthetic drugs relies on the Cytochrome P450 (CYP450) liver enzyme system. Since many anesthetic agents use the same metabolic pathways as THC and CBD, the presence of cannabinoids can either inhibit or induce enzyme activity, altering how quickly the body processes the drugs. Chronic cannabis use can upregulate this system, accelerating the metabolic degradation of drugs like propofol.
Accelerated drug clearance means that the anesthetic is broken down faster than expected, reducing its concentration in the bloodstream. Consequently, a higher dose of induction and maintenance drugs is often required to achieve and sustain the necessary depth of anesthesia. Studies have shown that chronic cannabis users may need doses of propofol that are 15% to 30% higher than those needed for non-users. This need for significantly higher drug quantities results from the chemical and physiological changes induced by cannabinoids on the central nervous system and liver metabolism.
Specific Clinical Risks During Procedures
The need for higher anesthetic doses introduces direct consequences in the operating room, making careful monitoring essential. The increased quantity of sedatives and induction drugs required places a greater strain on the patient’s cardiovascular system. This higher drug load increases the risk of complications, including undersedation and undesirable cardiovascular side effects.
Cannabis use independently affects the cardiovascular system, which can be exacerbated by anesthesia. Acute use can cause an increase in heart rate (tachycardia) and blood pressure, which may become unstable during the procedure. These fluctuations can be compounded by the vasodilatory effects of anesthetic agents, raising the risk of significant changes in blood pressure. For individuals with existing coronary artery disease, the risk of a heart attack is elevated in the hours following cannabis use.
The method of cannabis consumption, particularly smoking, presents a risk to the respiratory system. Inhaling cannabis smoke can cause irritation and inflammation in the airways, similar to or greater than that seen with tobacco use. This irritation can lead to airway hyperreactivity, increasing the chance of bronchospasm or laryngospasm during intubation or throughout the procedure. These respiratory complications can make securing a patient’s airway more challenging for the anesthesia team.
Essential Patient Actions Before Surgery
The most important action a patient can take before any procedure is to provide complete and honest disclosure of their cannabis use to the healthcare team. This includes detailing the type of product, the frequency of use, the method of consumption, and the date of their last use. This information is treated as confidential and is used solely to ensure the safest possible anesthetic plan, allowing the team to anticipate and mitigate potential interactions.
Current medical guidance on the timing of cessation varies, but it emphasizes a personalized consultation with the anesthesia provider. For patients who smoke cannabis, an abstinence period of at least two weeks is often recommended to reduce airway irritability and the risk of respiratory issues. While some guidelines suggest a minimum of 72 hours of abstinence before elective surgery, a longer period is generally safer, particularly for heavy users.
For patients who use cannabis daily or in high doses, a gradual tapering or cessation should ideally begin at least seven days before the scheduled procedure. Abrupt cessation of cannabis too close to surgery, particularly within 24 hours, can trigger acute withdrawal symptoms like anxiety, irritability, and changes in pain perception. Communicating this risk is important, as these symptoms can complicate both the pre-operative and post-operative recovery period.