The singer's family also said that the tests showed alcohol was present, but it hasn't yet been determined if it played a role in the singer's death.
The 27-year-old was found dead in her London home July 23.
A statement released Tuesday by spokesman Chris Goodman on the family's behalf said "toxicology results returned to the Winehouse family by authorities have confirmed that there were no illegal substances in Amy's system at the time of her death."
It said the family awaited the outcome of an inquest that is due to begin in October.
The Associated Press contributed to this report.