Life is pain cocooned within extended periods of contentment and the mundane.

At some point, we all have to contend with that exquisite suffering, which seems like it might consume us, but it's how we emerge from the blackness that ultimately defines us as strong, resilient creatures.

The embittered protagonist of Cake has been so deeply scarred - physically and emotionally - by her pain that she is toxic to everyone who orbits her.

In Daniel Barnz' film, this font of bile and foul-mouthed misery is portrayed with bedraggled hair and make-up disfigurements by Jennifer Aniston.

It's a compelling dramatic performance, stripped bare of vanity, which reminds us that the Los Angeles-born actress is much more than the romcom girl next door.

Unfortunately, Aniston's eye-catching work is the glistening cherry on top of a half-baked drama that proves increasingly hard to swallow.

If scriptwriter Patrick Tobin had treated his mix of misfit characters with more care and sieved out some of the implausible dramatic detours, Aniston would probably have secured her first Oscar nomination as Best Actress.

Claire Bennett (Aniston) survived the car crash that shattered her body but her road to recovery is agonisingly long and winding.

She can't sit or stand without enduring shooting pain, which she curbs by popping prescription medication like candy.

Her despairing husband Jason (Chris Messina) and friends have abandoned her, driven away by Claire's perpetual meanness - everyone except for her maid Silvana (Adriana Barraza), whose devotion to an uncaring, self-destructive boss is a complete mystery to everyone, including us.

"I pay her to care about me. It's not my fault she gets sentimental," observes Claire by way of a feeble explanation.

When Nina Collins (Anna Kendrick), a fellow member of a chronic pain support group, commits suicide, Claire develops a new addiction: gate-crashing the grief of Nina's husband Roy (Sam Worthington) and young son Casey (Evan O'Toole).

However, Roy doesn't intend to don his shining armour and makes this clear to Claire.

"I can't save you. I can barely save myself and my kid," he confides sombrely.

Cake is an uneven bake, distinguished by Aniston's committed performance and a warm, empathetic supporting turn from Barraza.

Even when the rest of Barnz' film crumbles, which it does frequently, their sisterly solidarity holds our interest.

Throwaway interludes with a hunky gardener (Manuel Garcia-Rulfo) and a man from the past (William H Macy) sit awkwardly with scriptwriter Tobin's efforts to insert Nina's ghost into proceedings.

Kendrick has fun as this spectral voice of waspish reason, berating Aniston's short-tempered, selfish harridan, who is acutely aware of the role she plays in her miserable fairy-tale existence.

"Tell me a story where everything works out in the end for the evil witch," sourly jokes Claire.

That story would be Cake.