Robbie's Red Bull addiction

Robbie Williams reportedly worked his way through 20 cans of Red Bull and over 30 espressos a day before entering rehab.

The singer, checked himself into a clinic in Arizona yesterday on his 33rd birthday, suffers from insomnia that often keeps him awake until 5am.

The debilitating condition has made it hard for Robbie to function in recent months and friends have commented that the star took prescription drugs "like Smarties".

"[Going to rehab] is the best present he could give himself," said Robbie's mum Jan.

"He's a very public figure and all the media attention at the moment is added pressure on him. I am not going out to visit Robbie yet. Rehab is all about being on your own. But once he gets better I will be over there like a shot."