When the single was not released, as planned, it came as no surprise. Still, a lot of people were disappointed because Dr. Dre had never promised a Detox single. Jay-Z spoke on the song and he said it should probably come some time before the end of May. With the end of May around the corner, "Under Pressure" has still yet to be released. Now, there is a likely answer to why this is so.
Eminem recently spoke on the single and he revealed why the song has yet to be released to the radio. Initially, Eminem had planned to use music he recorded last year when working on Relapse for his next album, Relapse 2. But, Interscope Records forced him to move on from the Relapse, so his music could not even be used. Quickly, Eminem came up with the concept for another album, Recovery, but he needed someone to help him. Had Dr. Dre released "Under Pressure," he would have had to go out and promote the song. There was no way he could do Eminem's album and promote himself.
Because he has always chosen Eminem first, Dr. Dre decided to help with Eminem's album and delay the release of "Under Pressure" until Eminem is ready to begin the next phase of his album.