The thought of flavor-of-the-month Amy Schumer, widely praised for her breakout Comedy Central series, teaming up with assembly-line raunch-master Judd Apatow may set the hearts of fans of each aflutter, but in the event “Trainwreck,” though hardly living down to its title, proves basically another trip down a familiar route. Still, the gender change, bright writing and acting from Schumer, a nice turn by co-star Bill Hader and a strong supporting cast combine to make the formula go down fairly easily.

At the start thirty-something Amy Townsend (Schumer) is definitely the child of her cantankerous father (Colin Quinn) in every respect. More than two decades earlier, as we see in a funny-sad flashback, he’d explained to her and her sister Kim that monogamy was unrealistic—which is why he and their mother were divorcing. It was just a device to explain away his philandering, of course, but though Kim dismissed his anti-moralizing and is now happily married to Tom (Mike Birbiglia), Amy has inherited dad’s cynical attitude. A heavy drinker and drug user, she indulges constantly in casual sex, mostly single-night stands, though as a kind of security blanket she maintains a relationship with Steven (WWE wrestling star John Cena), a dense, muscle-bound fitness freak who nonetheless has commonplace dreams of marriage and family that are destroyed when he learns of Amy’s freewheeling infidelity.

Amy’s job matches her lifestyle: she’s a writer at a sleazily glossy magazine called S’nuff, which specializes in the kind of snarky pop culture stuff that will make copies fly off supermarket checkout shelves. Assigned the task of doing a piece on Aaron Conners (Bill Hader), a sports doctor with lots of celebrity clients, by her imperious editor (a hilariously overbearing Tilda Swinton, showing us what Amy might become), she finds the good-hearted fellow goofily charming, and before long she’s inevitably torn between maintaining her selfish attitudes or trying to change for love.

The trajectory that “Trainwreck” will take is pretty much preordained; the difference is that instead of slob man-child Seth Rogen maturing as a result of an unplanned pregnancy in “Knocked Up,” we have a woman—brighter and more articulate but equally irresponsible and self-centered—becoming an adult by finding Mr. Right. One of the climactic moments in “Trainwreck” even involves a group hug reminiscent of the “Mary Tyler Moore Show” finale, although in this case it’s a familial one consisting of Amy, Kim, Tom and his quirkily endearing son Allister (Evan Brinkman). The picture also swerves periodically into more serious mode, most notably in an episode involving a sudden death and another centering on what legally would amount to rape—but in each case Schumer manages to leaven the sequences with dark humor.

What saves the movie from becoming nothing more than a tired retread, in fact, is the sharp writing and engaging cast. Schumer produces a steady stream of clever lines, not only for herself but for other characters as well, and she’s a deft physical comedian, particularly adept at finding facial expressions that reveal her reactions without words. Her screenplay does share with Apatow’s a tendency to opt for explicitness, especially of a sexual sort, from time to time just for shock’s sake, but she doesn’t make a habit of it, and there’s only a single throwing-up scene, which is way below the norm in this sort of fare. And the script has a somewhat shapeless quality, inserting digressions that may be amusing but are more like cadenzas than plot necessities. (One features scenes from an ersatz black-and-white movie, a pretentious piece called “The Dog Walker” starring Daniel Radcliffe and Marisa Tomei.) For the most part they work, but they draw the running-time out to more than two hours, and an elaborate final reconciliation sequence at Madison Square Garden is too silly and prolonged—though it will probably pay off with audiences that have come to expect whiz-bang endings, however contrived.

Schumer is also fortunate in her leading man: Hader is hardly the typical hunk, and he brings an easygoing affability to a guy who—let’s face it—is almost impossibly good-natured and tolerant of her foibles, and always willing to help (he gets an award from Doctors Without Borders, for goodness sake—an organization which Amy doesn’t even know about until his involvement is explained to her). The rest of the cast is equally winning. Quinn rants in his usual fashion, and Swinton plays a harridan to perfection (with Jon Glaser, Vanessa Bayer, Ronald Park and Ezra Miller contributing solid turns as other of Amy’s office colleagues), while Brie, Birbiglia and Brinkman manage to make likable character out of figures that could have been cloying. Veteran Norman Lloyd shows up as Quinn’s fellow rest-home resident, showing he can still deliver lines with the punch of a man half his age.

And the sports-related cameos are surprisingly agreeable, with folks like Tony Romo, Chris Evert and Marv Albert showing up briefly (along with, for some reason, Matthew Broderick). Among the more extended turns, Amar’e Stoudemire is a mite stiff in a sequence in which his knee is prepared to go under Dr. Conners’ knife, but Cena manages Steven’s verbal fumbling with disarming agility. Best of all, LeBron James contributes a funny version of himself as a matchmaking cheapskate; fans will particularly enjoy his one-on-one session with Hader, even if the payoff isn’t all you might wish. From the directorial standpoint “Trainwreck” shows Apatow becoming more skilled at framing shots and pacing scenes properly, though it’s difficult to tell how much of the credit rests with him rather than the cast, cinematographer Jody-Lee Lipes and editors William Kerr and Paul Zucker.

In fact “Trainwreck” represents something of a comeback for Apatow, as well as a promising big-time debut for Schumer. One hopes that both can stay on track from this point on.