Illustration of the molecular structure of sufentanil (C22.H30.N2.O2.S), a synthetic opioid analgesic (painkiller). It is approximately 5 to 10 times as potent as fentanyl and 500 times as potent as morphine. Due to its extremely high potency, it is mostly used during surgical procedures and critical care where quick pain relief is necessary. It is also used for post-operative pain management in patients who have a high tolerance to opioids due to long-term use. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), nitrogen (blue), oxygen (red) and sulphur (yellow).