Publicist Nicole Perna said Wednesday 28-year-old Nicole Richie checked herself into Cedars-Sinai Medical Center in Los Angeles.
Richie was in a Los Angeles courtroom earlier this week after asking for a restraining order against two celebrity photographers.
A judge granted that request.
Richie costarred with Paris Hilton on the television show "The Simple Life" and is the daughter of singer Lionel Richie.
She has since become a fashion and jewelry designer and occasional actress.
Richie gave birth to a son, Sparrow James Midnight Madden, in September.
She and her partner, rocker Joel Madden, have a daughter, Harlow, who turns 2 in January.