General anesthesia is, used for most major surgeries and can affect the entire body, including the brain and reflex functions. It carries more risks of side effects and complications than local or regional anesthesia, but they generally are minor, temporary, and easily managed. The most common general anesthesia side effects include headache, nausea, vomiting, blurry vision, and sore throat. These symptoms usually disappear as the anesthesia wears off. Post-surgery patients may also feel tired, drowsy, weak, or fuzzy-headed for several days after surgery, and are typically advised not to drive or operate heavy machinery for at least 24 hours.

One of the main causes of general anesthesia side effects is the method of administration. Sometimes an endotracheal (ET) tube is inserted into a patient's throat to help prevent aspiration. The insertion and removal of the tube can cause respiratory problems and injury or irritation to the throat and larynx. Hoarseness, coughing, gagging, and muscle spasms in the voice box or bronchial tubes in the lungs are all possible, but extremely rare.

An increase in blood pressure and heart rate also are common general anesthesia side effects, but don't normally cause lasting complications. Other typical general anesthesia side effects can include bruising, coordination problems and muscle pain. Shivering or trembling also is a very common side effect that occurs in about 40 percent of patients. Shivering is partly due to the heat loss that usually occurs in frigid-cold operating rooms, but also can be a direct result of the anesthesia — the body's temperature thermostat resets while under general anesthesia, allowing it to tolerate the colder temperatures. When a patient wakes from the anesthesia, the body's thermostat returns to normal and may react to a lingering low body temperature by shivering.

New drugs and better equipment have made general anesthesia increasingly more safe. Serious general anesthesia side effects and complications during surgery are rare, but possible. Allergic reactions, infections, lung problems, heart problems, and stroke are unlikely, but are potential risks. Malignant hypothermia is a rare, sometimes fatal, condition that can be triggered by anesthetics as well. The fear of waking up during surgery, called anesthesia awareness, is very common, but the chances of it actually happening are only about one in 14,000. The chance of dying after receiving general anesthesia is about 1 in 250,000, though this is rarely due to the anesthesia alone.

Though very rare, some serious side effects can occur after a patient undergoes general anesthesia — and not necessarily right away. Some patients may experience pale or yellow skin or eyes; back, leg, stomach, or abdominal pain; and severe headache or nausea as long as two weeks after surgery. Other complications may include black or bloody vomit or stool; weight loss or loss of appetite; unusual lethargy or weakness; and weakness in the wrists or fingers. If any of these complications arises, a visit to a doctor or emergency room is recommended.

Many factors, including a patient’s age and current health, play a part in how they will respond under general anesthesia. Heart, lung, circulatory, and nervous disorders may increase the risk of problems. Medical history, drug or food allergies, and previous reactions to anesthesia are important aspects that should be discussed with the doctor or anesthesiologist. Patients should also disclose the use of prescription medications, herbal supplements, over-the-counter drugs, alcohol, tobacco, or illegal substances.