The East 25th Street entrance of the William and Anita Newman Vertical Campus of Baruch College in the Gramercy section of Manhattan served as the entrance façade of All Saints Hospital at which Nurse Jackie and her colleagues work during the first three seasons. In the fourth season, the hospital's entrance façade was changed to Bellevue Hospital at East 27th Street and First Avenue.
The character played by Haaz Sleiman during the first season of the show was nicknamed Momo, but his actual name is Mohammed de la Cruz. Both his first and last names are essential elements of two different major world religions (Mohammed is the inventor of Islam, and "de la Cruz" means of the cross in Spanish, the cross being a foundational symbol of Christianity).
The trivia items below may give away important plot points.
Although they have stated from the very beginning that it wouldn't happen, co-creator Linda Wallem said they decided to get Jackie into rehab mainly because Edie Falco shared some concern about the character's influence. According to Falco, many people came up to her on the street and said, with excitement, that they used the same drugs as Jackie. Therefore a season in which Jackie is placed into rehab although not permanent, was deemed appropriate due to the series' continuing storyline.
Clyde Phillips, an executive producer and showrunner for Nurse Jackie, gave a June 2015 interview to Vareity in which he said that the show's writers started the final season with a completely different final scene in mind than the one that actually appeared in the last episode's final moments. Phillips described that alternate ending (which was never shot) as one in which Jackie heroically rushes back into the hospital as it is burning down to save a patient--but when she realizes she can only save herself, she escapes the burning building and then runs away from the scene, allowing everyone in her life to believe she died in the fire. But Phillips said that the writing staff decided against that ending because it focused "too much on the building and props and not enough about the character and the consequences of what she's done. About half-way through the season we had little trouble turning the boat around and going in that new direction."