In setting up the sex scenes, the actors were encouraged to improvise, but with their clothes on. Edward Zwick says that it is "colder" on a set because there are people all around, the camera, and other distractions. Therefore, the improvisation was useful in setting the scenes and shots for the actual shoot.
In designing the sex scenes, director Edward Zwick had the principals watch romantic comedies and sexually charged films - everything from Pillow Talk (1959) to 9 Songs (2004) to Last Tango in Paris (1972) - and talk about what turned them on. Then some of those shots and ideas were incorporated into the making of the scenes.
The anti-Parkinson's drugs Sinemet and Ropinirole mentioned in the film can cause sexual hyperactivity and hyperarousal in some patients as a side effect.
When Jaime is on the couch eating cereal at Maggie's house, the box reads "corn flakes". The label switches from facing the camera to facing away from the camera. Also, the box switches from the corn flake box to what appears to be a Honey Nut Cheerios box.
Jamie Randall: Sometimes the things you want the most don't happen and what you least expect happens. I don't know - you meet thousands of people and none of them really touch you. And then you meet one person and your life is changed forever.