Article written by
Dipak HemrajHead of Research and Education
Content reviewed by
Dr. Lewis JasseyMedical Director - Pediatric Medicine
Table of contents
Using cannabis can undoubtedly affect how anesthetics work, and this means that your anesthesiologist needs to know if you use cannabis before undergoing the medical procedure utilizing anesthetics.
Cannabis has a wide variety of effects on the body. As cannabinoids like to stick around in the body (they cling to fat cells), it is worth telling your physician about your use during your pre-operative exam as soon as possible. This way, the anesthesiologist can better understand what sort/s of drugs or drugs they need to use and how much. They do not want a negative interaction between the cannabis you use and any muscle relaxants, anticoagulants, anesthetics, sedatives, or opioids given before, during, or after your surgical procedure.
To minimize any unnecessary risk, give the medical professionals all the information they need upfront.
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Risks of Using Cannabis Before Going Under Anesthesia
Many people use cannabis to help their pain and reduce the prescription medications they need. However, there may be some risks when using medical cannabis before going under anesthesia, as the effects of two different substances can interact with one another. Some complications may arise, such as:
- Breathing difficulties. Smoked cannabis — inhaling cannabis through smoke can increase phlegm production cause breathing difficulties, coughing, and wheezing. Vaping doesn’t produce smoke, but you may still inhale ultrafine particle flavorings like diacetyl and heavy metals, so it is not necessarily safer. It is considered wise not to smoke any substance before going under anesthesia.
- Increased blood pressure. Cannabis has complex effects on the cardiovascular system and can increase heart rate and blood pressure in the short term and decrease them in the long term. The combination of increased heart rate and reduced blood pressure may increase the likelihood of a heart attack in some patient populations, so the anesthetist mustn’t give you medication that may increase your chances of having a heart attack.
- Heart failure. Cannabinoids like THC and terpenes like pinene have vasodilatory effects (i.e., they relax and widen blood vessels), but in the short term, they can have vasoconstrictive effects as well. Using vasodilators before surgery may increase the likelihood of heart failure.
- Ineffective anesthesia doses. In one study, those who used cannabis daily or weekly needed three times as much propofol to achieve adequate sedation for endoscopies.
- Increased potency of painkillers like opioids.Opioids may be used to treat operative pain, and surgeons are required to consider the patient’s needs and experience with opioids before their surgery even begins. Using cannabis can increase opioids’ effects (e.g., depress breathing further), so telling the surgical team can help them determine what dosage they may need.
For these reasons, an anesthetist must know if you use cannabis.
Should You Stop Using Cannabis Before Undergoing Anesthesia?
We cannot give any advice on when a patient should stop using medical cannabis with regards to anesthesia, as there are too many factors at play — like which anesthetics are being used, the type of treatment you’re undergoing — to give specific advice on when to stop using cannabis.
Some patients require medical cannabis to function at their best and reduce symptoms like chronic pain, cramps and spasms, and seizures. Suffering from such health problems can make it difficult to stop using the medication you need, so it is best to ask people on your surgical team for advice on when to stop using medical cannabis and take your needs into account.
Does Cannabis Affect Post-Surgery Recovery?
Anesthetics aren’t exclusively used in surgery, but their usage is most often associated. Chronic, post-operative, and post-surgery pain could be one area where medical cannabis shines, as it can help reduce or replace the need for more addictive opioids. Many patients use medical cannabis to reduce their intake of not only opioids but also sedatives, antidepressants, and recreational substances like alcohol and tobacco.
There is one study that shows some negative results. The study found that medical cannabis patients:
- Required more of the anesthetic, sevoflurane, for similar pain-numbing effects.
- Reported higher pain scores during the recovery stage of their surgery.
- Received more opioids per day while in hospital, with the typical stay being 2-3 days.
This is just one study involving 118 patients, and researchers did not include patients who suffered from chronic pain before their injury, which may affect the results.
Medical cannabis users who have built some tolerance to the cannabinoids they consume may be able to return to cannabis use sooner after their surgery compared to less experienced medical cannabis users. However, this is only a supposition, and most of the harms seem to occur in those who use cannabis on the day of their surgery.
When reviewing several clinical trials into account, there is moderate evidence that medical cannabis can help treat chronic pain. Other studies support the notion of “cannabinoid-induced analgesia” — pain relief due to cannabis use. Another study notes that cannabis exposure decreases the need for blood pressure support during general anesthesia in orthopedic trauma surgery.
Although there may be some risks and harms associated with cannabis use post-surgery, these may apply more to some cannabis-naive users or those who require cannabis for other health problems. There is little research in this area, though, so nothing can be stated for definite.
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Frequently Asked Questions
Does marijuana use affect dental anesthesia?
This depends very much on which type of anesthetic you’ll be given. Cannabis may interact more with sedatives, general anesthetics, and regional anesthetics, with less interaction with local anesthetics such as lidocaine. Local anesthesia is more common for dental operations, such as filling cavities, but some dental work may require stronger anesthetics. More research is needed in this area.
Should you tell your anesthesiologist if you smoke weed?
Marijuana has a sedative effect of interacting with anesthetics and those undergoing anesthesia. It’s important to tell your surgical team and anesthesiologist if you use cannabis, how often you last used it and what method of ingestion you use (e.g., smoking, vaping, edibles, tinctures). This way, the doctor can determine your needs with greater accuracy.
Can it be fatal to use cannabis before surgery?
It is possible that using cannabis before surgery can cause complications, even fatal ones, but it is important to note that there is little research into this area. Most negative results are in studies with small sample sizes where they do not differentiate between dose, method of administration, or frequency of cannabis use. Moreover, some physicians claim that medical cannabis is no different than accommodating other medications. However, this does mean that the anesthetist will need to know about and adjust for your cannabis use to make more informed decisions regarding medications and dosages.