The "Rehab" singer was released from Holborn police station after initially being declared "in no fit state" for an interview.
The British songstress had voluntarily turned herself in around 5 p.m. Friday after a man filed a report claiming Winehouse "headbutted" him outside a London pub April 23 when he tried to get her a cab.
A police spokesman told People that after a doctor decided Winehouse was not fit for an interview, she spent the night in the police station. The doctor gave the okay Saturday morning for the singer to be questioned.
"A 24-year-old woman today received a caution for common assault and has been released from custody," the police spokesman said, not releasing Winehouse's name because she was not charged with a crime.
According to MSNBC, a caution means that although Winehouse was not charged, the assault will remain on her record and could count against her if she ever faces similar charges in the future.
Winehouse spokesman Chris Goodman released a statement that said the singer "admitted to a common assault by slapping a man with an open hand and accepted a caution."
"Amy was fully cooperative with inquiries and apologized for the incident," the statement said. "She thanks the police for their professional handling of the matter."
