Mexhohexital was a drug in use on Earth during the early 21st century.
In 2004, Loomis stole some mexhohexital from a blood bank at which he worked to sedate his victims, whom he was delivering to the Xindi-Reptilians for whom he was working. (ENT: "Carpenter Street")
In the episode's final draft script, the drug is called methohexital, which is a real sedative. However, the spelling "mexhohexital" was clearly seen on its packaging. The same teleplay also indicated that a drug Loomis is shown injecting into Georgia Tandy's left arm, after sedating her with a chloroform-covered rag, was intended to be methohexital.