Don Suddaby (who plays himself in the film) is the actual British biochemist that has synthesized the pure oil (erucic acid) that was used to treat Lorenzo. He was born in the city of Hull, Yorkshire, where he has a street named after him - 'Suddaby Close' - which runs adjacent to 'Lorenzo Way'.
Michelle Pfeiffer was originally cast as Michaela Odone but dropped out in order to play Catwoman in Batman Returns (1992) a role that Susan Sarandon also expressed interest in. The script for "Lorenzo's Oil" was given to Sarandon but she steadfastly refused to read it until she knew that Pfeiffer was no longer participating in the film.
In a 2014 interview at the Florida Film Festival, Susan Sarandon said that Lorenzo's Oil was originally conceived and shot with the intent that as Lorenzo got sicker and sicker, the movie would fade from color to black and white. However, the production ran out of the money needed to process the film in that way, and the movie ended up being in color from beginning to end. She also said that this was actually the second movie in her career for which this had happened--that originally, the Rocky Horror Picture Show was supposed to be in black and white until the first appearance of Dr. Frank-N-Furter, when his red lips would have been the first item in color in the movie--but again, the production didn't have the money to process the film in that way, so the whole thing stayed in color.