The domino that sets off a cascade of falling pieces in "Why Stop Now" is a Catch-22 moment based on an incident witnessed by co-director Ron Nyswaner while working as a volunteer in a detox unit.

When Penny Bloom (Melissa Leo), a cocaine addict, is badgered by her son, Eli (Jesse Eisenberg), to enter rehab, she is turned away for lack of insurance and because her urine sample shows no signs of drugs. Surreptitiously advised that she will be admitted if she comes back with "dirty" urine, Penny and Eli do as suggested and go directly to her dealer, Sprinkles (Tracy Morgan), whose supply has run dry.

There is a deadline. Eli, a piano prodigy with his own substance-abuse problems, has an audition for an elite music conservatory that very afternoon.

Although none of the far-fetched shenanigans that follow match the story's initial conceit in real-life absurdity, the movie desperately piles on more and more silliness with a fundamental absence of credibility.

That wouldn't be a problem if "Why Stop Now" were a farce. But it aspires to be a semi-serious drama.