Understanding What Drugs Interact With Anesthesia: A Critical Guide

October 13, 2025 •

4 min read

An estimated 32% of ambulatory surgery patients use herbal supplements, many of which can negatively interact with anesthesia and increase bleeding risk. Understanding what drugs interact with anesthesia is therefore critical for surgical safety, as interactions can lead to severe complications like excessive bleeding, unstable blood pressure, or prolonged sedation.

Quick Summary

Many common prescription, over-the-counter, and herbal medications can cause dangerous interactions with anesthetic agents, potentially leading to complications like bleeding, high or low blood pressure, or prolonged sedation. Patients must fully disclose all substances to their anesthesiologist for safe perioperative care.

Key Points

Blood Thinners and NSAIDs: Anticoagulants and NSAIDs must be managed or stopped prior to surgery to prevent excessive bleeding.
Antihypertensives: ACE inhibitors and ARBs are often held on the day of surgery to prevent profound drops in blood pressure.
Psychiatric Medications: MAOIs and Lithium are often discontinued, while TCAs and SSRIs are generally continued to prevent withdrawal or relapse, requiring specific anesthetic adjustments.
Herbal Supplements: Many popular herbs like Ginkgo and St. John's Wort can increase bleeding risk or interfere with anesthesia and should be disclosed and often discontinued preoperatively.
Recreational Drugs: Substances like stimulants and chronic opioids can cause significant cardiovascular risks or alter pain management needs during and after surgery.
Full Disclosure is Key: Patients must provide a comprehensive list of all medications, including prescriptions, OTC drugs, and supplements, to their anesthesiologist for a safe procedure.

Why Medication History is Crucial for Safe Anesthesia

Before any surgical procedure, a thorough review of a patient's medication history is one of the most critical steps in planning for anesthesia. Anesthesiologists must be aware of all substances a patient is taking, including prescription drugs, over-the-counter medicines, herbal supplements, and recreational drugs. The combination of anesthetic agents with other medications can produce unpredictable and sometimes life-threatening effects, such as dangerous fluctuations in blood pressure, heightened risk of bleeding, or prolonged sedation. In some cases, a medication must be temporarily discontinued, while in others, the anesthesiologist simply needs to adjust their approach.

Blood Thinners and NSAIDs: A Major Bleeding Risk

Perhaps the most well-known medication interaction with surgery involves drugs that affect blood clotting. Anticoagulants and antiplatelet agents are designed to reduce the risk of thromboembolic events (e.g., blood clots), but this effect is highly undesirable during a surgical procedure where controlled bleeding is essential. Similarly, many common over-the-counter pain relievers can increase bleeding risk.

Drugs to Discuss with Your Doctor

Prescription Anticoagulants: Warfarin (Coumadin), apixaban (Eliquis), dabigatran (Pradaxa), rivaroxaban (Xarelto), and clopidogrel (Plavix). For these, a specific bridging plan might be necessary, where the patient is switched to an injectable anticoagulant like heparin for a short period.
Nonsteroidal Anti-Inflammatory Drugs (NSAIDs): Aspirin, ibuprofen (Advil, Motrin), and naproxen (Aleve) should generally be stopped 7-10 days before surgery.

Cardiovascular Medications: Managing Blood Pressure and Heart Rhythm

Patients with heart conditions or high blood pressure often take medications that require careful management during the perioperative period. Failure to adjust these can lead to serious cardiovascular events.

ACE Inhibitors and ARBs: Medications like lisinopril and losartan can cause severe drops in blood pressure (hypotension) when combined with anesthesia. Many protocols recommend holding these for 24 hours before surgery.
Beta-Blockers: Used for conditions like high blood pressure or heart failure, beta-blockers are often continued throughout surgery, as stopping them abruptly can cause heart rhythm problems.
Calcium Channel Blockers: Generally not held before surgery, but anesthesiologists should be aware of their use as they can affect cardiac function.

Psychiatric Medications: Balancing Risks and Withdrawal

Discontinuing psychiatric medications can lead to significant withdrawal symptoms or a relapse of the underlying condition. Many of these drugs also interact with anesthetic agents, requiring careful management.

MAO Inhibitors (MAOIs): This class of antidepressants can cause a hypertensive crisis if combined with certain anesthetic drugs or foods containing tyramine. MAOIs are often discontinued well in advance of surgery.
Tricyclic Antidepressants (TCAs): Can cause cardiac conduction issues and interact with vasopressors. They are generally continued, but the anesthesiologist must be informed.
SSRIs and SNRIs: These are typically continued through the perioperative period to prevent withdrawal. However, they can increase bleeding risk and, in rare cases, contribute to serotonin syndrome if combined with certain opioids.
Lithium: This mood stabilizer can prolong the effects of muscle relaxants and cause toxicity if a patient becomes dehydrated. It is often held 72 hours before surgery.

Herbal Supplements and Over-the-Counter Products

Because they are not regulated like pharmaceuticals, herbal supplements and certain over-the-counter products are a major concern. Patients may not even consider them when discussing medications with their doctor.

Common Supplements That Interact with Anesthesia

Ginkgo Biloba, Garlic, Ginseng: All can increase the risk of bleeding.
St. John's Wort: Can interfere with anesthesia and prolong its effects, and also poses a risk of serotonin syndrome.
Kava and Valerian Root: These can increase the sedative effects of anesthesia.
Vitamin E: Can increase bleeding risk.

For most supplements, it is recommended to stop taking them at least 1-2 weeks before surgery.

Recreational Drugs and Chronic Opioid Use

Recreational substances and chronic opioid use can significantly complicate anesthesia and pain management. Chronic opioid use can increase post-operative pain sensitivity and make pain harder to manage. Stimulants like cocaine or methamphetamine increase the risk of cardiac events during surgery. The anesthesiologist needs to know about any recreational drug use to properly assess the risks.

Comparison of Psychotropic Medication Management and Anesthetic Considerations


Medication Class	Perioperative Management	Key Anesthetic Considerations and Risks
MAO Inhibitors	Discontinue 7-14 days prior to surgery.	Hypertensive crisis with indirect vasopressors (e.g., ephedrine); Serotonin syndrome with opioids (e.g., meperidine); Avoid ketamine.
Tricyclic Antidepressants	Continue, unless a specific cardiac or other risk is identified.	Cardiac arrhythmias, QT prolongation; Exaggerated response to indirect vasopressors; Risk of postoperative confusion.
SSRIs/SNRIs	Continue throughout perioperative period.	Increased bleeding risk; Serotonin syndrome risk with certain opioids; Low risk of interactions overall.
Lithium	Discontinue 72 hours before surgery due to renal clearance concerns.	Prolonged neuromuscular blockade; Reduced anesthetic requirements; Risk of toxicity with dehydration or renal impairment.
Antipsychotics	Continue, as abrupt cessation increases relapse risk.	Orthostatic hypotension; Prolonged QT interval; Possibility of Neuroleptic Malignant Syndrome.

Conclusion: Communication is the Best Anesthetic

In summary, the complex interplay between different drugs and anesthetic agents requires careful and honest communication between the patient and their healthcare team. Patients should never assume a medication, supplement, or over-the-counter product is harmless. Full disclosure allows the anesthesiologist to formulate the safest possible plan, minimizing the risks associated with adverse drug interactions and ensuring a smoother surgical process. Always bring a complete, up-to-date list of all medications to your preoperative appointment.

For more information on patient safety in surgery, visit the American Society of Anesthesiologists website.

Frequently Asked Questions

Common prescription blood thinners like Warfarin, Eliquis, Pradaxa, and Xarelto often need to be stopped several days before surgery under a doctor's supervision. Over-the-counter NSAIDs like aspirin and ibuprofen also need to be discontinued, typically 7 to 10 days beforehand.

It depends on the medication. ACE inhibitors and ARBs are often stopped 24 hours before surgery to prevent severe hypotension. However, beta-blockers and most other heart medications are usually continued to maintain a stable heart rhythm.

Herbal supplements are not heavily regulated and can have active compounds that interfere with anesthesia. Many, like Ginkgo, Garlic, and Ginseng, increase bleeding risk. Others, like Kava and Valerian, can increase sedative effects.

Specific interactions depend on the type. MAOIs pose a risk for hypertensive crisis and serotonin syndrome. TCAs can cause cardiac issues. SSRIs and SNRIs, while safer, can increase bleeding risk. Your anesthesiologist should always be informed.

Omitting a medication from your history can have serious consequences. Anesthesiologists rely on this information to tailor their plan. Interactions can cause dangerous complications like unstable blood pressure, excessive bleeding, or delayed recovery. It's crucial to be as thorough as possible.

Chronic opioid users often require higher doses of anesthesia and may experience heightened pain sensitivity after surgery, making pain control more challenging. It's essential to disclose all opioid use, including prescribed and illicit, to your care team.

You should provide a complete list of all medications, including dosages and frequency, along with any vitamins, supplements, or recreational drug use. You should also discuss any allergies, past reactions to anesthesia, and pre-existing medical conditions.