Amy Winehouse was released on bail last night after being questioned by police over drug offences, Scotland Yard said.
The singer left Limehouse police station in east London at 10.30pm after arriving by appointment at 1pm.
The 24-year-old was arrested over video footage published in January which appeared to show her inhaling fumes from a crack pipe.
The 'Rehab' singer was driven away in a silver Mercedes people carrier. She made no comment to waiting reporters.
Scotland Yard said she was bailed to return on a date in May.
A spokesman for Scotland Yard said a 24-year-old from Camden was arrested in connection with the alleged possession of a controlled drug.
"This is in connection with an investigation connected to footage passed to the Metropolitan Police on January 22," he said.
On January 22, a newspaper published pictures apparently showing the Rehab singer smoking crack cocaine.
Footage obtained by The Sun newspaper appeared to show her inhaling fumes from a crack pipe.
The star was also shown apparently snorting ecstasy and cocaine and admitting downing six Valium.
Winehouse's spokesman said in a statement: "Amy Winehouse voluntarily attended a London police station today by appointment.
"She was arrested in order to be interviewed and is co-operating fully with inquiries.
"The interview relates to a video handed to police earlier this year."
It is the singer's second run-in with police in as many weeks.
Two weeks ago, she received a police caution and apologised for slapping a man during an early hours row.
The Grammy award winner was arrested on April 25 and spent the night in a cell at Holborn police station in central London before being questioned.
The 24-year-old was alleged to have headbutted a good Samaritan who hailed her a taxi outside a bar and punched a second man.
But a spokesman said she "slapped" a man with an open hand and accepted the caution.
Last month it emerged Winehouse, whose husband Blake Fielder-Civil is in jail awaiting trial on charges of conspiracy to pervert the course of justice, is worth £10 million.
Her appearance and behaviour have sparked concerns about her wellbeing from friends and family.
In February, it appeared that things were turning around for her when she won five prizes at the Grammy awards, despite being absent from the ceremony.
The acclaimed musician's problems began to spiral publicly last year.
She was admitted to hospital last August after a reported overdose of heroin, ecstasy, cocaine, ketamine and alcohol.
Fans were shocked to see the 'Back to Black' singer bloodstained and covered in scratches, wearing blood-soaked ballet shoes, and with bruises to her neck, bandages on her arms and make-up smeared down her face after she quit rehab with her husband.
The singer, the daughter of a north London taxi driver, married Fielder-Civil in Miami, Florida, in May last year.
Her father, Mitch Winehouse, once said he was so concerned about his daughter he wrote a eulogy he expected to deliver at her funeral.
The beehived star, currently recording the theme tune for the next James Bond film, recently received three nominations for the prestigious Ivor Novello songwriting awards.
She became the first artist to receive two nominations for the top prize, Best Song Musically and Lyrically.