I am an anesthesiologist. To an anesthesiologist, fentanyl is as familiar as a Philips screwdriver is to a carpenter; it is an indispensable tool in my toolbox. It is the most commonly used painkiller during surgery. If you’ve had surgery, it is more likely than not that you have had fentanyl. Fentanyl is used to blunt airway reflexes and to place the breathing tube into the trachea with minimal coughing. It is the potent analgesic that prevents pain from the surgeon’s scalpel while your body sleeps under anesthesia. It is also the painkiller that allows you to wake from anesthesia without feeling existential pain in the immediate recovery room once the gases are turned off. Fentanyl is used to enable millions of people to undergo major surgery in the United States every day.