Before anesthesia, there are several things that can increase your risk of serious complications, from eating too close to your procedure to taking certain supplements or medications. Most of these mistakes are preventable if you know the timeline. Here’s what to avoid and why it matters.
Eating and Drinking Too Close to Surgery
The single most important rule before anesthesia is fasting. When you’re under general anesthesia, the reflexes that normally keep food and liquid out of your lungs stop working. If your stomach isn’t empty, its contents can travel back up into your throat and slide into your airways. This is called pulmonary aspiration, and it happens in roughly 1 out of every 2,000 to 3,000 surgeries. Nearly half of patients who aspirate during surgery develop a lung injury such as pneumonitis or pneumonia. In severe cases, as little as 50 milliliters of stomach contents (a few tablespoons) can cause respiratory failure or cardiac arrest.
The general fasting framework works like this: stop eating solid food at least six to eight hours before your procedure. Clear liquids like water, black coffee, tea without milk, and pulp-free juice are typically allowed up to two hours beforehand. The American Society of Anesthesiologists actually encourages patients to drink water and sugary clear liquids up to two hours before anesthesia to stay hydrated and maintain energy. Fatty or fried meals take longer to leave the stomach, so you may be asked to fast even longer if you ate a heavy dinner the night before. Follow whatever specific instructions your surgical team gives you, as these can vary by procedure.
GLP-1 Medications Like Ozempic and Wegovy
If you take a GLP-1 receptor agonist for diabetes or weight loss, this deserves special attention. These drugs work partly by slowing down how fast your stomach empties, which means food can sit in your stomach far longer than normal. That raises the risk of aspiration even if you followed standard fasting rules.
The American Society of Anesthesiologists recommends that patients on a daily GLP-1 medication skip it on the day of surgery. If you take a weekly version (like semaglutide), hold your dose for a full week before the procedure. This applies regardless of whether you take the medication for diabetes or weight loss, and regardless of the dose or type of surgery.
Pain Relievers and Blood Thinners
Over-the-counter pain relievers are some of the most commonly used medications, and several of them interfere with blood clotting. Taking them too close to surgery increases the risk of excessive bleeding during and after your procedure.
Ibuprofen (Advil, Motrin) and diclofenac (Voltaren) should be stopped at least one day before surgery. Naproxen (Aleve) needs a longer window of four days. Aspirin, which has a stronger and longer-lasting effect on platelets, should be stopped 7 to 10 days before surgery. These timelines reflect how long each drug continues to affect your blood’s ability to clot after your last dose.
Prescription blood thinners have their own schedules. Warfarin (Coumadin) requires at least five days off before a procedure. Newer blood thinners need two to three days depending on the specific drug. Your surgeon or anesthesiologist will give you exact instructions, but the key point is this: don’t assume you should keep taking these medications as normal just because they were prescribed. And equally important, don’t stop a prescribed blood thinner on your own without confirming with your care team, since stopping certain medications abruptly carries its own risks.
Herbal Supplements and Vitamins
Many people don’t think of supplements as “real” medications, but several common ones affect bleeding, blood pressure, or how your body processes anesthesia drugs. The safest approach is to stop all nonessential supplements at least two weeks before surgery.
Garlic supplements and hawthorn carry the strongest evidence for increasing surgical bleeding on their own, even without blood thinners. Ginkgo biloba and chondroitin-glucosamine are also considered high risk. A longer list of supplements with moderate bleeding risk includes turmeric, melatonin, echinacea, fish oil, flaxseed, ginger, chamomile, milk thistle, ashwagandha, evening primrose, and St. John’s Wort. St. John’s Wort is particularly worth flagging because it can also change how your liver processes anesthesia drugs, potentially making them stronger or weaker than expected.
The most important thing is to tell your anesthesiologist about every supplement you take, even if it seems harmless. Many patients forget to mention supplements during pre-operative interviews because they don’t consider them medications.
Smoking and Vaping
Smoking before surgery creates problems on multiple fronts. Carbon monoxide from cigarettes binds to your red blood cells and reduces how much oxygen your blood can carry. Nicotine raises your heart rate and blood pressure, increasing the heart’s demand for oxygen at a time when supply is already limited. Together, these effects make it harder for your body to handle the stress of anesthesia and recover from surgery.
Carbon monoxide levels drop significantly within just 12 hours of your last cigarette, and nicotine clears within about two hours. So even stopping the night before surgery provides some measurable benefit to oxygen delivery. That said, longer is better. Patients who quit more than two months before surgery have significantly fewer pulmonary complications than those who quit later. Those who stop six months or more before surgery have the same complication risk as people who never smoked at all.
Vaping carries similar concerns because of nicotine’s effects on the cardiovascular system, even without the carbon monoxide component of traditional cigarettes. If you can’t quit weeks in advance, stopping even 12 to 24 hours before your procedure still helps.
Drinking Alcohol
Showing up to surgery with alcohol in your system is dangerous enough that your procedure will almost certainly be postponed. Alcohol acts as a depressant on the nervous system, and when combined with anesthesia drugs, it amplifies their sedating effects in unpredictable ways. Anesthesiologists would need to significantly reduce drug doses for an intoxicated patient, making it harder to maintain a safe, stable level of anesthesia.
For people who drink regularly, stopping abruptly before surgery introduces a different risk: alcohol withdrawal. Withdrawal can cause seizures, dangerous spikes in heart rate and blood pressure, confusion, and delirium. These complications are two to five times more common in surgical patients than in other hospitalized patients. If you drink heavily or daily, it’s critical to be honest with your anesthesia team so they can monitor for withdrawal and manage it safely. Patients with harmful alcohol intake also face higher rates of postoperative infections, irregular heart rhythms, bleeding, and longer hospital stays.
Nail Polish, Jewelry, and Piercings
During surgery, a small clip on your finger continuously monitors your blood oxygen levels by shining light through your fingernail. Nail polish, especially gel manicures, can interfere with these readings. Dark colors like black and purple cause the most interference, producing unreliable oxygen measurements. Gel polish is particularly problematic because it can make readings falsely high, potentially masking a dangerous drop in oxygen that your team needs to catch immediately. You’ll typically be asked to remove polish from at least one or two fingernails. If removal isn’t possible, the monitoring clip can sometimes be placed on an earlobe or toe instead.
Metal jewelry and piercings are generally asked to be removed before surgery. While published case reports of burns from retained piercings during electrosurgery are essentially nonexistent with modern equipment, jewelry can still interfere with imaging, get in the way of the surgical team, or pose a choking hazard if a piece comes loose. If you have a piercing you can’t easily remove, let your team know in advance so they can plan around it.
Shaving the Surgical Area
If your surgery involves an incision, do not shave the area yourself beforehand. Razors create tiny nicks and cuts in the skin that become entry points for bacteria, raising the risk of surgical site infection. CDC guidelines are clear on this: hair should not be removed at all unless it will physically interfere with the operation, and if it does need to go, it should be clipped with electric clippers by the surgical team immediately before the procedure. Shaving with a razor at home the night before is one of the worst things you can do for infection risk.
What to Tell Your Anesthesiologist
Beyond avoiding specific things, one of the biggest pre-anesthesia mistakes is withholding information. Your anesthesiologist needs a complete picture to keep you safe. This includes every medication and supplement you take, how much alcohol you drink (honestly), whether you smoke or vape, any recreational drug use, past reactions to anesthesia, and whether you might be pregnant. Anesthesia is not one-size-fits-all. Doses and drug choices are adjusted based on your specific health profile, and surprises in the operating room are the last thing anyone wants.