Many common medications, supplements, and recreational substances can interfere with anesthesia, either by increasing bleeding risk, causing dangerous drops in blood pressure, or changing how much anesthetic you actually need. Some need to be stopped days or even weeks before surgery, while others require your anesthesia team to adjust their approach on the spot. Here’s what you should know about the major categories.
Blood Thinners and Antiplatelet Drugs
Blood-thinning medications are among the most carefully managed drugs before any surgery. Warfarin is typically stopped 5 days before a procedure. Clopidogrel, which irreversibly affects platelets, needs to be stopped 5 to 7 days before elective non-cardiac surgery. Newer oral blood thinners like rivaroxaban, apixaban, and dabigatran follow a different schedule: they’re usually held 24 hours before low-risk procedures and 48 hours before high-risk ones, though people with reduced kidney function may need to stop them 4 days out since the drugs clear more slowly.
Aspirin also reduces the blood’s ability to clot. A large trial of over 10,000 patients undergoing non-cardiac surgery found that those given aspirin had a 23% higher odds of major bleeding compared to placebo. Whether aspirin needs to be stopped depends heavily on the type of surgery and why you’re taking it. If you take aspirin because you’ve had a heart attack or a stent placed, stopping it carries its own serious risks, so the decision involves weighing both sides.
Blood Pressure Medications
ACE inhibitors and ARBs, two of the most widely prescribed blood pressure drug classes, interact with general anesthesia in a way that can cause stubborn, hard-to-treat drops in blood pressure during surgery. Continuing these medications on the morning of surgery is associated with roughly a 30% increase in the relative risk of intraoperative hypotension. When blood pressure drops severely under anesthesia, it can sometimes resist the usual medications used to bring it back up.
For this reason, many anesthesiologists prefer that patients skip their ACE inhibitor or ARB on the morning of surgery, particularly for procedures under general anesthesia. If you do hold the medication, it should be restarted as soon as possible afterward to keep your underlying blood pressure and any heart or kidney conditions well controlled.
Antidepressants and Psychiatric Medications
MAO inhibitors, an older class of antidepressant, pose some of the most serious risks during anesthesia. They block an enzyme that breaks down both serotonin and adrenaline-like chemicals in the body, which means certain drugs used during surgery can trigger unpredictable spikes in blood pressure or a dangerous buildup of serotonin. Common surgical drugs that raise adrenaline-like activity indirectly, such as certain medications used to support blood pressure, should be avoided entirely when MAO inhibitors are on board.
SSRIs, the most commonly prescribed antidepressants, carry a different but related concern. About 14% of patients undergoing major surgery are taking an SSRI. The primary risk is serotonin syndrome, a condition marked by high blood pressure, rapid heart rate, agitation, and in severe cases, dangerously high body temperature. This becomes a real threat when SSRIs are combined with other drugs that boost serotonin levels. Several pain medications used during and after surgery do exactly that, including tramadol and certain cough suppressants. SSRIs also slow the liver’s ability to break down some of these drugs, which can cause them to build up to higher-than-expected levels in the body.
Chronic Opioid Use
If you’ve been taking opioid pain medications daily for more than two weeks, your body has likely developed tolerance. This has significant implications for anesthesia and pain control. During surgery, you may need up to 20% more than your usual daily opioid dose to account for the pain of the procedure itself. After surgery, you’ll almost certainly have higher pain levels and greater analgesic needs than someone who doesn’t take opioids regularly. Breakthrough pain is more common and tends to feel more intense.
Your anesthesia team needs to know your exact daily opioid intake. The baseline goal is to provide at least 50% of your typical daily dose throughout the surgical period just to prevent withdrawal, on top of whatever is needed for surgical pain. This applies whether you’re having general anesthesia or a regional block. Many teams use a multimodal approach for opioid-tolerant patients, combining nerve blocks, non-opioid pain relievers, and ketamine alongside continued opioid therapy to get pain under control.
GLP-1 Weight Loss and Diabetes Drugs
Semaglutide, tirzepatide, liraglutide, and other GLP-1 receptor agonists have become extremely common for both diabetes and weight loss. These drugs slow stomach emptying, sometimes dramatically. The concern is that food or liquid can remain in your stomach even after you’ve followed standard fasting instructions, raising the risk of vomiting and inhaling stomach contents into your lungs during anesthesia.
The American Society of Anesthesiologists recommends holding daily GLP-1 medications on the day of surgery and weekly formulations (like the weekly semaglutide injection) a full week before the procedure. This applies regardless of whether you’re taking the drug for diabetes or weight loss. For urgent surgeries where you can’t wait, the anesthesia team will treat you as having a full stomach and take extra precautions. If your procedure can’t be delayed and you’ve been on a GLP-1 drug, switching to a clear liquid diet for at least 24 hours beforehand can help reduce the amount of retained food in your stomach.
Herbal Supplements
Several popular herbal supplements increase bleeding risk in ways that matter during surgery. Garlic supplements inhibit platelet clumping, and case reports document significant postoperative bleeding in people taking them. The risk compounds when garlic is combined with aspirin, ibuprofen, or warfarin. In one case, a man experienced a spontaneous spinal blood clot and surgical bleeding linked to heavy garlic supplement use.
Ginkgo biloba has a similar antiplatelet effect. Reports describe spontaneous eye bleeding in a man taking both ginkgo and aspirin. Aloe vera supplements, which contain salicylate compounds (the same family as aspirin), have been linked to excessive bleeding after oral surgery. In one case, aloe also interacted with a common inhaled anesthetic, causing abnormal bleeding during the procedure itself. Because supplements aren’t regulated as strictly as medications, many people don’t think to mention them before surgery, but they can be just as relevant as prescription drugs.
Recreational Drugs and Cannabis
Recent cocaine use is one of the most dangerous situations for anesthesia. Cocaine raises circulating stress hormones, increases blood pressure and heart rate, stiffens arteries, and can trigger coronary artery spasm. The risk of heart attack increases 24-fold in the first hour after cocaine use. Under anesthesia, these effects create an unstable cardiovascular picture where dangerous heart rhythms, including rapid irregular heartbeats and ventricular arrhythmias, become far more likely. Most surgeons and anesthesiologists will postpone elective surgery if recent cocaine use is suspected.
Methamphetamine carries similar risks: hypertension, coronary vasospasm, heart attack, and arrhythmias. Emergency department data shows rapid heart rate as the most common heart rhythm problem in methamphetamine users. MDMA (ecstasy) adds hyperthermia to this list, which complicates temperature regulation under anesthesia.
Cannabis affects anesthesia differently. Regular users (more than once per week) need higher doses of the common induction drug propofol to achieve satisfactory sedation. In one study, cannabis users required significantly more propofol for successful airway device placement than non-users (314 mg versus 263 mg on average). This tolerance effect means that if your anesthesiologist doesn’t know about your cannabis use, the initial dose may be insufficient, potentially leading to lighter-than-intended sedation or awareness during the procedure.
NSAIDs Like Ibuprofen
Over-the-counter pain relievers like ibuprofen and naproxen affect platelet function, though their effects are reversible and shorter-lived than aspirin’s. The evidence on whether they meaningfully increase surgical bleeding is surprisingly mixed. A study of 161 tonsillectomy patients found no significant difference in blood loss or reoperation rates between those given IV ibuprofen and those given placebo. A larger surveillance study of 300 surgical patients found zero cases of perioperative bleeding with preoperative ibuprofen.
That said, certain procedures are considered higher risk for bleeding complications, including tonsillectomy, prostatectomy, cardiovascular surgery, and major orthopedic operations. For these, many surgeons still ask patients to stop NSAIDs several days beforehand as a precaution, even though the definitive evidence supporting that practice across all surgery types is limited. For lower-risk procedures, the concern is generally smaller.