You use cannabis products. 

You’re about to have an anesthetic. 

Should you tell your anesthesiologist or not? Read on . . . 


Cannabis, or marijuana, is used by approximately 2.7-4.9% of the world’s population, making it the most widely used illicit drug on Earth. Cannabis is also one of the most widely used drugs in the United States, where an estimated 22 million people over the age of 12 use cannabis products each year. 


Fifty years ago, in 1970, the Drug Enforcement Agency (DEA) regulated all cannabis products in the United States to Schedule 1 classification. Schedule 1 drugs have no accepted medical use and have a high potential for abuse. Other Schedule I drugs include heroin, LSD, mescaline, psilocybin, and ecstasy.  This classification of cannabis as a Schedule I drug made it impossible for American-based researchers to conduct research studies on cannabis products on humans. Typically a new medication must clear specific hurdles with the DEA before it is approved for public usage. At present the recreational use of marijuana is legal in 11 states: Alaska, California, Colorado, Illinois, Maine, Massachusetts, Michigan, Nevada, Oregon, Vermont and Washington, and also in Washington, D.C.

A problem exists because cannabis is categorized as an abuse drug that was not able to be studied, and has now been legalized without appropriate research. The physiology and pharmacology of cannabis in humans is also difficult to study because a) there are many different cannabinoids present in marijuana products, each with variable effects, and b) the drug can be either inhaled or ingested orally. If the DEA eventually removes cannabis from the DEA Schedule I list, then scientific prospective clinical trials can be done to better evaluate the implications of cannabis use.


The most potent psychoactive product in the marijuana plant is delta-9-tetrahydrocannabinol, or THC.

THC is found in the flowering buds of the plant, and to a lesser degree in the leaves, stems, and seeds. The half-life of THC in the body is 5-13 days. Modern cultivation improvements have increased the THC content of cannabis. The average marijuana cigarette in the 1970s contained 1 – 3% THC, the average marijuana cigarette in the 1990s contained 6 – 20% THC, and some currently available strains have up to 33% THCButane hash oil extracts may have a THC concentrations as high as 90%.  The effects of cannabis are difficult to predict because the THC concentration in any delivered dose depends on both the THC concentration of the product, and the route of delivery.

CBD, short for cannabidiol, is a product marketed for antianxiety and chronic pain problems. CBD is not psychoactive, meaning it doesn’t have a strong effect on cognitive brain activity and doesn’t cause the central nervous system high associated with THC. Like all cannabis products, CBD is still classified as a Schedule 1 drug by the DEA. To date I’m unaware of any data that CBD interacts with anesthetics in any important way. 


To an anesthesiologist, a patient’s three most important physiologic systems are the brain, the heart, and the lungs. These are also the systems most effected by cannabis. Inhaled cannabinoids are rapidly distributed within the vessel-rich group of organs in the human body (the brain, lungs, heart, kidney, and liver), and effects are seen within seconds to minutes after an inhaled dose. The effects of orally ingested cannabinoids may be delayed up to 1 to 2 hours. 


The most well known effects of marijuana involve the central nervous system, and include euphoria, sedation, and relaxation. Adverse side effects include apathy and lack of motivation.  Some users report reduced anxiety with cannabis use, but there are reports of worsened anxiety leading to paranoia or psychosis with cannabis use.There have also been case reports of acute psychosis after rapid ingestion of high doses of oral THC. Due to the central nervous system effects of cannabis, marijuana use has been implicated in motor vehicle accidents. Studies have shown a dose-dependent effect of acute cannabis administration on slowing the reaction time of drivers, and causing them to weave between traffic lanes. This is worsened by co-administration of marijuana with ethanol.These marijuana-plus-or-minus alcohol users may present to anesthesiologists for emergency surgical procedures related to traffic accidents. 


The acute cardiac effects of cannabis administration include rapid heart rates (tachycardia) and the peripheral dilation of blood vessels, which causes low blood pressure.  A study showed that tobacco smokers with stable angina who never smoked cannabis developed angina with exercise significantly faster after smoking cannabis.  A second study showed a 5-fold increased risk of a heart attack (myocardial infarction or MI) in the first hour following cannabis smoking, compared to a 24-fold increased risk of MI in the hour following cocaine ingestion. The elevated risk of heart attack in cannabis users is thought to be due to a combination of the increased heart rate, the lower blood pressure, and the increase in cardiac work.  In the United States, cannabis use disorder has not been associated with any change in overall perioperative morbidity, mortality, length of hospital stay or costs, but cannabis use disorder is associated with an increased risk of postoperative myocardial infarction


Studies show bronchodilation and decreased airway resistance with either inhaled or ingested THC, but marijuana smoking can also result in airway hyperreactivity similar to that seen with tobacco smoking. Marijuana can be more irritating to airways because it burns at a higher temperature than tobacco. Cannabis is commonly smoked in hand-rolled and unfiltered cigarettes, or “joints,” introducing high concentrations of carcinogenic chemicals and irritants into the airways and lungs. Vaping cannabis oil promotes the inhalation of respiratory carcinogens and irritant compounds which can cause lung injury. Characteristics of cannabis smoking such as prolonged and deep inhalation, a shorter joint butt, and the higher combustion temperature, may result in greater carboxyhemoglobin  levels and tar retention in the airways. The chronic effects of inhaled marijuana include cough, bronchitis, and emphysema similar to those seen in chronic tobacco smokers.


The cannabis withdrawal syndrome is validated as a clinical entity in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) as well as in the International Classification of Diseases (ICD) systems. Cannabis withdrawal syndrome can develop within a day after stopping high-dose chronic cannabis use. The symptoms include irritability, aggression, anxiety, insomnia, disturbed dreams, depressed mood, weight loss, abdominal cramping, sweating, fevers and chills.  


In every cannabis using patient, the anesthesia preoperative evaluation should include assessment of the psychologic, cardiac, and pulmonary systems in order to minimize any risk of a perioperative complication. 

It’s important for the anesthesiologist to know the duration, frequency, and route of their patient’s cannabis use, as well as the time of most recent intake. Anesthesiologists should seek to identify patients as new or chronic cannabis users. If a patient exhibits any central nervous symptoms of acute cannabis intoxication, it’s important to assess the patient for symptoms of escalating anxiety, paranoia, or psychosis, as these symptoms may predict a violent emergence from anesthesia. The current lab testing methods assaying for plasma or urine cannabis levels do not provide effective quantitative data on cannabis intoxication. The history and physical examination by a physician are more important than a toxicology screen. Drug screening for cannabis is not currently a standard of care in preoperative medical evaluation.

Prior to urgent anesthetics on a patient with acute cannabis intoxication, the anesthesiologist will 1) consider delaying the induction of anesthetic induction until the resolution of tachycardia and/or low blood pressure, and 2) conduct a preoperative evaluation for chronic marijuana smokers similar to that used for chronic tobacco smokers. This includes questioning the patient regarding exercise tolerance, shortness of breath, chest pain, and listening to the lungs for evidence of chronic bronchitis or emphysema. 


When attending to a cannabis user, the anesthesiologist must be aware that:  a) cannabis consumers may have an increased tolerance to anesthetics,  b) cannabis consumers have an unknown cross-tolerance to the anesthetic agents, c) cannabis consumers have an increased risk of myocardial infarction (MI or heart attack) within one hour after use, and d) cannabis consumers may have increased airway reactivity (i.e. wheezing, coughing, shortness of breath, or asthma symptoms).

In a prospective, randomized, single-blinded study, thirty male patients using cannabis more than once per week and 30 nonusers aged 18-50 years had anesthesia induced with propofol. The dose of propofol required for successful placement of a laryngeal mask airway (LMA) tube was significantly higher in the cannabis group than in nonusers

Researchers studied 27 patients undergoing elective orthopedic surgery who were randomly allocated to high dose cannabis (6 patients), low dose cannabis (8 patients), active placebo (6 patients) and placebo (7 patients). The cannabis drugs were administered 20 minutes before induction of general anesthesia in a double-blind fashion. During inhaled anesthesia, the researchers examined the patient’s bispectral index (BIS index, i.e. an intraoperative brain EEG level that measures depth of  general anesthesia). The average BIS values were significantly higher (i.e. the patients were not as deeply anesthetized) in the high dose cannabis treatment group. The researchers concluded that for cannabis consuming patients, one cannot rely on the EEG-BIS monitoring for the purpose of determining the patient’s anesthetic depth. An inference from this data is that cannabis patients were more tolerant of maintenance inhaled general anesthesia doses than non-cannabis users.

Because cannaboids are Schedule I drugs, and the effects of cannabis have been more thoroughly studied in animals. Studies in mice and rats showed cannabinoid-induced analgesic tolerance to morphine. There have been no similar studies in humans published to date. 


Following surgery, cannabis users report higher pain scores, worse sleep, and require more narcotics than non-cannabis users.  In Jamaica, a prospective randomized study was carried out on 73 patients who underwent elective surgery. There were 42 cannabis users and 31 non-users. The cannabis users required significantly higher supplemental Demerol (meperidine) doses after surgery.  (J Psychoactive Drugs. 2013 Jul-Aug;45(3):227-32)

As discussed previously, after surgery physicians should remain vigilant to cannabis withdrawal symptoms in chronic cannabis users.


If you are the patient, when you present for surgery and anesthesia, will the nurses and doctors specifically ask you if you use cannabis or marijuana? Perhaps not. Current routine preoperative evaluation usually includes the question “Do you use any street drugs?” Nearly 100% of patients answer “No.” As discussed above, 22 million people in the U.S. use cannabis, yet very few will admit this on a preoperative questionnaire. Why? I believe most people do not want to be identified as using a drug which is still deemed illegal by the federal government. Most people do not want “marijuana user” to be part of their medical history problem list. They may fear the moniker of “marijuana user” following them onto some digital database, damning them in future insurance applications or legal actions. I believe most people do not believe identifying themselves as cannabis users makes any difference to their doctors and nurses. Per the discussions above, there are important reasons for an anesthesiologist to know if you use cannabis. But if you are a cannabis user, will you reveal the truth?

Cannabis is currently legal and commonly used in multiple states in America. The drug has specific effects on the brain, heart, and lungs which can affect your health during or after an anesthetic. 

For your own welfare, be honest and discuss your cannabis use with your anesthesiologist prior to surgery. 


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