A Mouthful of Air opens with a warning: “The following film may be upsetting to people with a history of depression and anxiety.” The story of a young mother subsumed by paralyzing feelings of inadequacy would be troubling to anyone, but that doesn’t necessarily make it involving. Though it’s not without cinematic touches and affecting, sometimes harrowing moments, and even with a convincingly fragile and unmoored Amanda Seyfried at its center, the drama is often hampered by an instructive sensibility that gives it the air of a feature-length PSA.

Seyfried plays children’s book author Julie, living a seemingly charmed upper-middle-class life ...