Morphine, fentanyl, alfentanil, and meperidine are the most widely utilized shivering medications, with meperidine being the most effective. Other commonly used agents include chlorpromazine (Thorazine) and promethazine (PMS-PM). None of these drugs has been shown to be more effective than another. In fact, some studies have suggested that using multiple agents together may be more effective than any single drug alone. Shivering is caused by small electrical signals that are sent from nerves located in the muscles. These signals cause the muscles to contract, causing a jerky movement. The brain receives this signal through special receptors called nicotinic acetylcholine receptors. When this type of receptor is stimulated by one of the above-mentioned medicines, it causes the body to react by producing a chill. This is why adding these medicines back to their liquid form or injection form will help reduce or prevent shivering. There are several reasons why patients may experience shivering under general anesthesia. One reason is that removing the protective layer of skin that covers the surface of the body allows heat to escape more easily. Under normal circumstances, heat is lost through the skin, but when you're under general anesthesia, this loss mechanism is disabled.