Amy Winehouse has been questioned by police in connection with a video apparently showing her smoking a crack-cocaine pipe.
Amy Winehouse went into rehab shortly after the video emerged
The singer has not been arrested, but was interviewed under caution and police said inquiries were continuing.
A Scotland Yard spokesman said officers had interviewed a 24-year-old woman in relation to an allegation of unlawful possession of a controlled drug.
The video was posted online by the Sun newspaper last month.
In the video, the Back To Black singer appears to say she has taken "six valium", before lighting up and inhaling from a pipe.
The video was reportedly filmed at her London home.
At the time, her record company Universal said: "We are deeply disappointed and upset by these latest revelations and are doing everything we can to offer Amy our full support in dealing with her problems."
Ms Winehouse has been in a rehabilitation clinic in London since 24 January, days after the video emerged.
She temporarily left the clinic on Monday to apply for a visa at the US embassy ahead of her planned performance at the Grammy Awards in Los Angeles on Sunday.
But her spokesman said "no decision" had been made about the appearance.
She has six Grammy nominations, including for record, album and song of the year.
Her application for a visa will not be simple because of her drugs record.
Last October she was arrested and fined in Norway for possession of cannabis. She is planning to appeal against the fine in a Norwegian court later this month.