I can't believe You care more about your stupid re-election than you care about all our lives!?
~ Leah to her boss Phlegmming after seeing what he truly is
Leah is a hard-working and serious female cell who wants to do what's right. She disliked Osmosis Jones at first, but she grew warm to him and started to care for him later on. Leah is very kind to her friends. She is also very self-righteous as she cares about Frank's health and all of blood cells within his body while wanting Frank to fix his relationship with his daughter.
Role in the film
She was first seen at her office where she told the Mayor about his opponent for the Mayor's Office, Tom Colonic, and Colonic's campaign video, and asks him about Frank's health.
Later on, she was sent to get a cold pill named Drix and while she's waiting, she notices that Osmosis was flirting with her, which she wasn't interested in and thought very little of him.
She wasn't seen again until she was at the Mayor's Office where Drix and Osmosis came in and was curious about Osmosis's story (the one when he first saw a virus named Thrax).
She believes him and tells the Mayor to cancel the trip to Buffalo so Frank will get better to be safe, but the Mayor doesn't want to cancel the trip because of his re-election and what the trip means if he wins and stays in office.
After Ozzy and Drix apparently kill Thrax and his henchmen in The Zit Club at the cost of popping it and ruining a chance by Frank to go on a father/daughter hiking trip by having Shane's teacher, Mrs. Boyd, lift the restraining order she took out on him after humiliating her some time ago when he threw up on her during the school science fair, which led to Frank losing his job at the pea soup factory when his supervisor learned of it when a photo of what happened appeared on the front page of the newspaper, infuriating him, Leah is back at the Third Precinct as Mayor Phlegmming confronts Ozzy on his actions, and when he still argues that Frank's health is more important than some stupid chicken wing trip, Phlegmming fires him in a fit of anger, refusing to own up to the severity of the situation out of the chance of losing his re-election. Leah is shocked by the Mayor's harsh decision and is deeply concerned for Ozzy as he sadly departs after turning in his gun and badge after being dishonorably discharged, feeling sorry for him.
Later on, she was seen again back in Cerebellum Hall after realizing that something is wrong in the Hypothalamus and told the Mayor that Osmosis was right about Thrax. When Phlegmming still refuses to believe Ozzy was right, Leah confronts him in a fit of anger, telling him off at how he only cared about his re-election rather than all their lives, and she angrily left to find out what's going on in the Hypothalamus, and later got kidnapped by Thrax.
When she got kidnapped, Ozzy and Drix rescue Leah and confront Thrax, who leaves Frank's mouth after causing Frank to sneeze using pollen bombs. With Thrax's escape, Leah fears they're doomed, but Ozzy refuses to let Thrax get away.
Ozzy is launched out after him by Drix. When Ozzy and Thrax fight on one of Shane's eyeballs and end up on Shane's false eyelashes, which she was wearing atop her natural ones, after she blinks, Ozzy recovers Thrax's bracelet that contained all the stolen Hypothalamus chromosomes from his previous victims.
During the fight, Thrax threatens to break his own record by killing Shane next, but Ozzy tricks him into getting stuck on Shane's false eyelash and falling into a vessel of alcohol below where he dissolves.
During this time, the situation becomes even more dangerous when the temperature in Frank's body hits 108 degrees, causing Frank to go into cardiac arrest. Watching from the uvula in Frank's mouth, with no sign of Ozzy, Leah fears he's not going to make it and breaks down sobbing in Drix's arms as Frank flatlines, while Ozzy's Chief hangs his head in defeat as well, accepting Frank is doomed.
Just as doctors begin to give up, Frank is revived when Ozzy returns to Frank via one of Shane's crying tears with the DNA chain containing the missing hypothalamus chromosome. It is quickly rushed to the Hypothalamus and reinstalled, reducing Frank's temperature back to a stable 98.6 degrees and resuscitating him, though during his short term of being deceased, he saw his wife Maggie, who wanted him to tell Shane that she said "Hi" from the afterlife.
Ozzy is reinstated into "Immunity" with full privileges, Ozzy and Drix are declared heroes with the Chief of Police giving Ozzy his job back.
While Osmosis was planning on extending Drix's time in Frank with the help from the hemorrhoid, Leah returns his affections and told him "Come here, baby. I'm still Jonesin for little more Osmosis."
Then, she kisses him on the lips which Osmosis was shocked at, but happily kissed back.
For some unknown reason, Leah does not appear in Ozzy & Drix.
Leah is the only female cell to be one of the main characters.
Leah bears a resemblance to Vicki Vale from Batman, part of the DC Universe.
Sherri Howard, Holly Robinson, Camryn Manheim, Paula Abdul, Nicole Kidman, Halle Berry, Cameron Diaz, the late Anna Nicole Smith, Julie Benz, Reese Witherspoon, Joely Fisher and Meg Ryan were all considered for the role of Leah Estrogen.
Osmosis Jones walks into the Chief's office and says "Brandy! I mean, Leah. Why are you here?" He is speaking to the mayor's aide Leah, who is voiced by Brandy Norwood. The flubbed line was acted so well that it was left in because it felt pleasingly funny.