The pop star is said to be addicted to anti-depressants.
In a statement, his spokeswoman confirmed: "Robbie Williams has today been admitted into a treatment centre in America for his dependency on prescription drugs."
While she would not reveal where, he is believed to be at the exclusive but "hardcore" Meadows clinic in Arizona - where outside contact is banned, along with alcohol, sugar, cigarettes and caffeine.
Unlike other centres - including The Priory, which he has already tried - the £2,000-a-night Meadows has a tough, no-frills approach.
It is officially a Level 1 Psychiatric Acute Hospital and specialises in a "12-step" treatment of serious disorders, from schizophrenia to heroin addiction.
The news follows a string of setbacks for the former Take That star, who has confessed to bouts of depression as well as drug and alcohol habits.
American model Lisa D'Amato, who says she had a relationship with Williams, was recently quoted as saying that he used anti-depressants.
She told a newspaper: "It was clear he was struggling with his mind. He doesn't drink but he needs antidepressants to get him through the day. A lot of the time he seemed on edge."
Last year, Williams appeared in the BBC documentary The Secret Life Of The Manic Depressive, where he confessed to beginning to take anti-depressants a year after becoming sober.
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What better anniversary gift could we have than Robbie Williams's acknowledgement that Seroxat is beautiful? Speaking on Sarah Cox's radio show last week, he revealed that SSRIs have pulled him back from depression. "I took too much ecstasy, to tell you the truth," he said. "When you take E, your brain releases an awful amount of serotonin the chemical in the brain that broadly correlates with happiness and it makes you go, Great.' Use it all up and your brain's got nothing to bathe in." SSRIs have restored his serotonin to normal levels (or as normal as it gets for a billionaire rock-god).
Are you listening Glaxo SmithKline?
Are you listening Dr Ian Hudson, Alistair Benbow?
Speaking on BBC One's Panorama programme, Dr Alastair Benbow, head of European clinical psychiatry at GlaxoSmithKline, admitted that people could have misunderstood the information on patient leaflets which said the drug was not addictive.