Officers grilled the singer, 24, at North London's Capio Nightingale clinic about a video that appears to show her using crack cocaine.
'She was not arrested,' says a source. 'She is co-operating with police.'
Cops seized the footage after it was leaked last month.
The investigation could set back Amy's plans to go to the US for Sunday's Grammy Awards ceremony.
'The timing of this isn't great,' the source tells The Sun. 'She is desperate to go to The Grammys and needs to show US officials she is taking her rehabilitation seriously.'
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