"I Don't Believe You" is set in common time and played in the key of A-flat major. The guitar and piano are used for the background music, while Pink's voice follows the A♭ —Fm7—Cm—D♭—A♭ chord progression. Pink explained on her website that, lyrically, the song is about pleading for reconciliation, and is her favourite song from Funhouse "because it's just so naked. It's like taking a deep breathe and saying, 'Here I am. Take me. Take your best shot'." She went on to explain that:

"The first thing that comes to my mind with I Don't Believe You is me standing in the vocal booth listening... Actually in the control room listening to this song, tears running down my face, just like 'fuck, really?' It's the vulnerable weak side of me that I don't let out very often. And it's [sighs], yeah it's that song. And I love it, I love it. I just love it, it's very near and dear to me."

Jonathan Keefe from Slant Magazine praised the song, its sparse electric guitar riff, and Pink's "phenomenal vocal turn that is both vulnerable and accusatory", while New York Times reporter Jon Caramanica claimed "I Don't Believe You" swells like a classic soul ballad, as Pink pleads for a lover to reconsider walking away. On another side, Christian Hoard of Rolling Stone magazine gave a negative review, claiming the song is a "goopy ballad", which makes the singer sound like "just another big-voiced chart-buster", and that she has shown more personality on previous singles.

"I Don't Believe You" is Pink's single with the lowest peak in the United Kingdom. It failed to reach the top forty due to physical single was cancelled. In the U.S. & Canada, the track has sold around 115,000+ in digital downloads, but failed to chart on the Billboard Hot 100, making I Don't Believe You her only single from Funhouse not to have higher charting. In Australia, the song reached number twenty-three on the sales chart and was the number-one most added track to the radio on its debut week of release. In the Europe, "I Don't Believe You" reached top forty in most countries with its highest peak in Portugal, where the song reached number one.

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Wikipedia