Emily Blunt would wear bloodshot contact lenses for the scenes in which she's heavily inebriated. She also wore prosthetics on her cheeks to make them look slightly plumper.
Emily Blunt was at the beginning stage of pregnancy at the start of filming. She kept this from the cast and crew except for her friend, co-star Justin Theroux. Director Tate Taylor only found our towards the end of filming when, filming a scene of Rachel showering, he noticed her bump and confronted her, asking if she'd withheld information that he should have known. Blunt eventually had to tell him, and he agreed to keep it secret. By the time filming ended in February 2016, she was in her fifth month of pregnancy.
By 2016, the source novel was the fastest-selling adult novel in history.
Emily Blunt's confession in the Alcoholics Anonymous meeting was unrehearsed. Blunt's nervousness and discomfort is completely genuine.
One of the main criticisms fans had with the casting of Emily Blunt was that she was too attractive for the role of a broken and chronic alcoholic Rachel Watson. The makeup artists got around this by extensively studying the skin of actual alcoholics and applying makeup to make her look more exhausted and washed out with dark circles under her eyes and puffy cheeks. The fact that Blunt was pregnant during filming helped with the effect.