Abstaining from cannabis before surgery is a non-negotiable safety measure mandated by surgical teams. Cannabis use, whether recreational or medicinal, introduces unpredictable variables that complicate anesthesia administration. These interactions affect drug metabolism, cardiovascular stability, and respiratory function, placing the patient at higher risk during and immediately after the operation. A mandatory period of abstinence is required to ensure the surgical team can safely manage the patient.
How Cannabis Affects Anesthesia Drug Dosing
A primary concern is that chronic cannabis use leads to tolerance to sedative and analgesic medications used during surgery. The active compound, tetrahydrocannabinol (THC), interacts with the body’s endocannabinoid system, creating cross-tolerance with anesthetic agents. This tolerance means higher-than-normal doses of induction drugs, such as propofol, are needed to maintain unconsciousness. Regular cannabis users may require 15% to over three times the standard dose of propofol for adequate sedation.
This increased medication requirement raises the risk of complications, including prolonged sedation or adverse drug reactions. THC is processed in the liver by the cytochrome P450 (CYP) enzyme system. Many surgical and anesthetic drugs, including opioids, share these metabolic pathways. Interference can alter the breakdown rate of these medications, leading to unpredictable concentrations in the bloodstream. Chronic users often require significantly higher amounts of inhaled anesthetics, highlighting the depth of this drug tolerance.
Increased Risk of Respiratory Complications
Inhaling cannabis, whether by smoking or vaping, creates chronic irritation and inflammation within the airways, presenting a significant challenge during general anesthesia. Cannabis smoke contains toxic substances, and the deep inhalation technique increases the delivery of harmful chemicals to the lungs. This chronic exposure often results in symptoms resembling chronic bronchitis, including a persistent cough, wheezing, and excessive sputum production.
The inhalation process can also cause acute swelling of airway tissues, such as uvular edema (swelling of the tissue at the back of the throat). This localized swelling can make the placement of the breathing tube (intubation) extremely difficult. A reactive airway state increases the risk of bronchospasm—a sudden tightening of the muscles around the airways—during the procedure or upon extubation. Furthermore, an irritated airway increases the risk of gagging or choking, which can lead to aspiration pneumonia if stomach contents enter the lungs.
Impact on Heart Rate and Blood Pressure
Cannabis use directly influences the cardiovascular system, which can be unstable in the operating room environment. THC can cause significant fluctuations in heart rate and blood pressure that are difficult for the anesthesiologist to manage. Acute cannabis use typically causes a sympathetic response, resulting in tachycardia (an elevated heart rate) that can increase by 20% to 100%.
This elevated heart rate and blood pressure stress the heart, raising the risk of a myocardial infarction (heart attack) shortly after use. Chronic use can sometimes lead to the opposite effect: hypotension (a drop in blood pressure) and bradycardia (a slowed heart rate). Anesthesia relies on stable vital signs, and these cannabis-induced fluctuations compromise the surgical team’s ability to maintain a safe state, especially during procedures involving major blood loss.
Post-Surgical Pain and Recovery Challenges
The use of cannabis before surgery complicates recovery by making post-operative pain management difficult. Chronic cannabis users frequently report higher pain scores following an operation, often linked to cannabis-induced hyperalgesia (increased sensitivity to painful stimuli). Due to tolerance, patients often require significantly larger doses of standard pain relievers, including opioids, to achieve adequate pain control.
One study found that cannabis users needed a 23% increased dose of post-operative morphine compared to non-users, increasing the risk of opioid-related side effects like excessive sedation. Furthermore, regular users may experience an increased risk of post-operative nausea and vomiting (PONV). The combination of increased pain and higher medication requirements introduces difficulties that can lengthen hospital stays and hinder recovery.