Understanding What Drugs Interfere with Anesthesia

October 10, 2025 •

5 min read

According to a survey, 22% of patients undergoing surgery have used herbal medicines, and many do not report this to their healthcare providers. This highlights a crucial safety concern, as a variety of prescription, over-the-counter, and recreational substances can significantly interfere with anesthesia and lead to serious complications.

Quick Summary

This article details various types of medications and supplements that can cause complications with anesthesia. It covers blood thinners, antidepressants, heart and blood pressure drugs, diabetes medications, and herbal supplements. Patients are advised on which drugs may need adjustments or temporary cessation before a procedure.

Key Points

Blood-Thinning Agents: Anticoagulants, NSAIDs, and some herbal supplements like ginkgo and fish oil increase the risk of bleeding and must often be discontinued before surgery.
Psychiatric Medications: MAOIs pose a risk of hypertensive crisis and serotonin syndrome, requiring specialized anesthetic management, while lithium can become toxic due to renal clearance changes.
Cardiovascular Drugs: Certain blood pressure medications, like ACE inhibitors and ARBs, may be held before surgery to prevent severe hypotension, while others, like beta-blockers, are often continued.
Diabetes Management: Medications such as GLP-1 agonists and SGLT-2 inhibitors carry specific risks, including delayed gastric emptying and ketoacidosis, and require careful timing and management prior to anesthesia.
Herbal and Recreational Substances: Undisclosed use of herbal supplements (Kava, Valerian) and recreational drugs (cocaine, alcohol) can lead to unpredictable and dangerous interactions, from prolonged sedation to cardiac events.
Disclosure is Critical: Providing your anesthesiologist with a complete and accurate medication history is the most important step a patient can take to prevent complications.

Anesthesia is a carefully controlled process, and the body's response to anesthetic agents can be dramatically altered by other substances. Understanding what drugs interfere with anesthesia is critical for anyone facing a surgical procedure. The potential risks range from bleeding complications to unstable blood pressure, altered sedative effects, and life-threatening reactions. For this reason, a thorough and honest disclosure of all substances, including those seemingly harmless, is essential.

Blood-Thinning Medications and Their Risks

One of the most significant concerns during surgery is the risk of excessive bleeding. Many medications, both prescription and over-the-counter, can inhibit the blood's clotting ability and interact dangerously with anesthesia.

Prescription Anticoagulants and Antiplatelets: These are powerful blood thinners used for conditions like cardiac stents or coronary artery disease. Examples include warfarin (Coumadin), rivaroxaban (Xarelto), apixaban (Eliquis), dabigatran (Pradaxa), and clopidogrel (Plavix). These typically must be stopped several days before surgery, and in some cases, patients are transitioned to a shorter-acting injectable anticoagulant. Regional anesthesia, such as an epidural, is often avoided in patients on anticoagulants.
Nonsteroidal Anti-Inflammatory Drugs (NSAIDs): Common NSAIDs like ibuprofen (Advil, Motrin) and naproxen (Aleve) have antiplatelet effects that increase bleeding risk. Most over-the-counter NSAIDs should be stopped days before surgery, though specific instructions depend on the drug and procedure. Acetaminophen (Tylenol) is generally considered a safe alternative for pain relief.
Herbal and Vitamin Supplements: Several supplements have blood-thinning properties and should be discontinued 1-2 weeks before surgery. These include vitamin E, fish oil, garlic, ginkgo biloba, and ginger.

Psychiatric Medications and Neurochemical Effects

Antidepressants and other psychotropic drugs can have complex and sometimes severe interactions with anesthetic agents, affecting blood pressure, heart rate, and brain chemistry.

Monoamine Oxidase Inhibitors (MAOIs): These are antidepressants known to have potentially fatal interactions with certain anesthetic drugs, leading to severe hypertension or serotonin syndrome. Indirect-acting vasopressors and opioids like meperidine are typically avoided. MAOIs are often continued until the day of surgery, but the anesthesiologist must be aware to use compatible anesthetic agents.
Selective Serotonin Reuptake Inhibitors (SSRIs): Generally considered safe to continue, but a small increased risk of bleeding has been observed. Combining SSRIs with certain opioids like tramadol can trigger serotonin syndrome.
Tricyclic Antidepressants (TCAs): Can lead to cardiac complications, including arrhythmias and prolonged QT intervals. They can also increase the risk of postoperative sedation and delirium when combined with other anticholinergic drugs.
Lithium: This mood stabilizer has a narrow therapeutic window and is excreted renally. Dehydration and other medications used perioperatively can increase lithium to toxic levels, which is why it's often held 72 hours before major surgery.

Cardiovascular and Diabetes Medications

Pre-existing conditions related to the heart, blood pressure, and diabetes require careful medication management before anesthesia to prevent serious hemodynamic shifts and metabolic complications.

ACE Inhibitors and Angiotensin Receptor Blockers (ARBs): These blood pressure medications are often held 24 hours prior to surgery to prevent a significant drop in blood pressure during anesthesia.
Beta-Blockers and Calcium Channel Blockers: These are typically continued through the day of surgery to manage heart rate and rhythm.
GLP-1 Agonists (e.g., Semaglutide): Used for diabetes and weight loss, these drugs can slow gastric emptying, increasing the risk of vomiting and aspiration during anesthesia, even after fasting. Patients are usually advised to stop taking them in advance.
SGLT-2 Inhibitors: Used for type 2 diabetes, these drugs can increase the risk of euglycemic ketoacidosis under surgical stress and fasting. They are typically held several days before surgery.

Herbal Supplements and Illicit Drugs

Herbal remedies and recreational drugs are a frequent cause of unexpected and dangerous anesthetic complications. Many patients do not consider them medications and fail to report their use.

Herbal Supplements: Kava, valerian root, and St. John's wort can all prolong sedative effects. Others, like ginseng and ginkgo biloba, can increase bleeding risk. Ephedra can cause heart rate and blood pressure instability.
Recreational Stimulants: Cocaine, methamphetamine, and amphetamines increase the risk of cardiac events due to their effects on the cardiovascular system. Chronic use may also deplete endogenous catecholamines, making patients resistant to standard vasopressors.
Alcohol: Chronic heavy alcohol use can increase anesthetic requirements and put the patient at risk for withdrawal symptoms. Acute intoxication can intensify sedative effects and complicate monitoring.
Cannabis/CBD Oil: These can affect heart rate, blood pressure, and pain control during and after surgery.

Comparison of Common Medication Interactions


Medication Type	Potential Anesthesia Complication	Perioperative Management	Key Considerations
Anticoagulants	Excessive bleeding, hematoma risk with regional anesthesia.	Stop several days before surgery; may switch to short-acting injectable.	Do not stop without consulting prescribing doctor and surgeon.
Antidepressants (MAOIs)	Serotonin syndrome, hypertensive crisis.	Continue perioperatively with special anesthetic precautions; avoid certain opioids and vasopressors.	Involve psychiatrist in care plan; ensure full disclosure.
ACE Inhibitors/ARBs	Severe hypotension during anesthesia.	Typically hold morning dose on day of surgery.	Beta-blockers and other cardiac meds are usually continued.
Herbal Supplements	Prolonged sedation, bleeding risk, hemodynamic instability.	Discontinue 1-2 weeks prior to surgery.	Many patients forget to report; be proactive in asking.
GLP-1 Agonists	Increased aspiration risk due to slowed gastric emptying.	Hold based on dosage schedule (e.g., 1 week before surgery for weekly dose).	Follow instructions precisely even after required fasting period.
Opioids/Benzos	Excessive sedation, respiratory depression.	Dosages are adjusted; close monitoring is critical.	Can have synergistic effects with anesthetics; risk increases with dose.

The Critical Importance of Preoperative Disclosure

It is imperative to provide your healthcare team with a complete and accurate medication history, including all prescriptions, over-the-counter drugs, herbal supplements, vitamins, and recreational substances. Many patients underestimate the significance of these interactions or fail to disclose them out of fear or forgetfulness. However, the consequences of withholding this information can be severe, leading to significant postoperative complications or jeopardizing the patient's safety during the procedure. The American Society of Anesthesiologists (ASA) recommends patients inform their anesthesiologists about all supplements and, in many cases, stop taking them at least two weeks before a surgical procedure.

Your anesthesiologist uses this information to create a personalized anesthetic plan that accounts for potential interactions and minimizes risks. They can adjust anesthetic dosages, select alternative medications, or implement different monitoring strategies to ensure your safety. Open communication is the cornerstone of safe and effective anesthesia care. Your surgical team needs your full partnership to navigate these complex pharmacological interactions successfully. For more detailed information on anesthetic management, reputable sources like the Anesthesia Patient Safety Foundation are invaluable.

Conclusion

Numerous drugs, from common NSAIDs and antidepressants to herbal supplements and recreational substances, have the potential to interfere with anesthesia. These interactions can lead to predictable side effects, like an increased risk of bleeding with anticoagulants, or more complex reactions, such as severe blood pressure changes with psychiatric medications or stimulants. By understanding which substances pose a risk and providing a complete medical and medication history to your care team, you play an active and vital role in ensuring a safe and successful surgical outcome. Always consult with your doctor or anesthesiologist well in advance of a procedure to review your medication plan.

Frequently Asked Questions

You should stop taking over-the-counter NSAIDs like ibuprofen (Advil) and naproxen (Aleve) several days before surgery due to their blood-thinning effects. Acetaminophen (Tylenol) is generally safe, but always confirm with your doctor. You should also report any herbal supplements and vitamins.

Yes, some blood pressure medications, such as ACE inhibitors and ARBs, can cause significant drops in blood pressure when combined with anesthesia. Your doctor will likely instruct you to hold the morning dose before surgery. Others, like beta-blockers, are usually continued.

Most antidepressants are typically continued in the perioperative period to prevent withdrawal symptoms. However, MAOIs require special management due to the risk of dangerous interactions with certain anesthetic agents and opioids. It is crucial to inform your care team of your specific medication.

Yes, the American Society of Anesthesiologists recommends stopping herbal and dietary supplements at least two weeks before surgery. Many, like ginkgo and St. John's Wort, can affect bleeding, sedation, and interactions with anesthetic drugs.

Certain diabetes drugs, like GLP-1 agonists (e.g., Ozempic, Wegovy) and SGLT-2 inhibitors, have specific risks. GLP-1 agonists can delay gastric emptying, increasing aspiration risk, while SGLT-2 inhibitors can cause metabolic complications. Your doctor will provide a specific plan for holding these medications.

Serotonin syndrome is a potentially life-threatening condition caused by excessive serotonin activity in the brain. It can occur when certain antidepressants, particularly MAOIs and SSRIs, interact with opioids like meperidine and tramadol, or antiemetics like ondansetron, which may be given during or after surgery.

Recreational drugs like stimulants (cocaine, methamphetamine) can cause heart rate and blood pressure fluctuations during anesthesia. Chronic use can also affect the body's response to medications. Anesthesiologists need this information to ensure patient safety and to prepare for potential complications.