The two-year-old daughter of Jude Law and Sadie Frost has been treated in hospital after swallowing part of an ecstasy tablet at a children's party.
Police said they were called by hospital staff after a toddler spent the night under observation on a ward after swallowing the drug.
Iris Law had a stomach pump and brain scan following the incident at an exclusive club in London's West End.
The actions of Frost, 34, prevented Iris from swallowing the entire tablet. Law, 29, was alerted as he was filming in the US, The Sun newspaper said.
A Scotland Yard spokesman said: "We were called at 4.11pm Saturday afternoon by a London hospital regarding a two-year-old female child that was believed to have swallowed half a tablet of ecstasy.
"The child had been attending a children's party on Saturday where she was believed to have picked up a tablet that had been left on the floor of the premises on Old Compton Street. The premises had been used as a bar and nightclub on the Friday.
"It is believed that the child's mother discovered the two-year-old with an obstruction in her mouth. She managed to retrieve one half before it could be ingested.
"An ambulance took the child to the hospital where she was kept in for observation overnight. She was released on Sunday morning. The tablet has been confirmed as ecstasy," he said.
A police source said there was no suggestion that Iris's parents were guilty of neglect, adding: "There are no plans to take action against the parents of the victim. This is being considered as an unforeseen accident outside the parents' control."