Morphenolog is a drug used to alleviate pain.
In 2371, Julian Bashir instructed Jabara to give Bareil Antos two ccs of morphenolog after he experienced severe pain. (DS9 episode: "Life Support")
In 2379, morphenolog was used in combination with asinolyathin by the USS Titan's medical team to alleviate Olivia Bolaji's pain during the birth of her child. (TTN novel: Taking Wing)