Additional reporting by Jessica Goebel

The floppy-haired boy we first came to love in “Ten Things I Hate About You” and “3rd Rock from the Sun” has long since graduated to more adult material with flicks like “Brick,” “Mysterious Skin” and “The Lookout.” Next year, Joseph Gordon-Levitt will try to keep the momentum going by broaching a very sensitive subject, in the family drama “Uncertainty.”

“It’s about a couple trying to decide whether to keep a pregnancy,” Levitt explained. The story depicts two versions of the same Fourth of July in New York City, presenting alternative series of choices revolving around that thorny issue.

Levitt’s lover in “Uncertainty” is played by Lynn Collins, whose previous credits include small roles in such varied fare as “The Lake House” and “Bug.” “She’s an amazingly skilled, inspiring artist,” Levitt raved of his co-star, who has been sharing time with him recently on the film’s New York set.

Such thespian prowess was critical for this project, considering the challenging method by which the film was shot: “It was entirely improvised,” Levitt revealed. Further clarifying that writing/directing/producing duo Scott McGehee and David Siegel constructed a loose script on purpose, Levitt said that it was then up to the actors to make up many of their lines on the spot. “The four of us would kind of come up with the details of each scene, each day,” he enthused.

But it seems one hot-button issue isn’t enough for Levitt; next year he also stars in “Stop Loss,” a movie that centers on an Iraq War veteran (played by Ryan Phillippe) who refuses orders to return for another tour of duty.

Last year’s well-received “Brick,” along with this upcoming slate of weighty films, seems to indicate that Levitt has some heavy days ahead of him. “Uncertainty” is on target for a late 2008 release.