The British company that makes Nurofen Plus painkillers recalled the tablets Friday because of suspected sabotage involving the use of drugs used to treat psychosis.
The Reckitt Benckiser company said there have been five reported cases of other manufacturers' medicines found in boxes of Nurofen Plus.
"Sabotage is suspected and we are working with the police on a formal investigation to find the person or persons responsible," the company said in a statement.
Consumers are being urged to return any packs of the painkiller to a pharmacy, said Dr. Aomesh Bhatt, Medical Director of Nurofen Plus.
Distribution has been halted after some of the tablets were found to contain a drug often used to treat psychosis and schizophrenia.
"We are taking this matter extremely seriously and have decided to recall all packs of Nurofen Plus as the most prudent course of action in the current circumstances," Bhatt said.
The company said the recall is limited to U.K. supplies of the medication.
In a statement on Thursday, Britain's medicines regulator issued a warning about the drug. The agency said it received reports of the prescription drug Seroquel found in packages meant to contain Nurofen Plus, a codeine-containing painkiller. It had no details on how the mistake might have happened.
Experts said a single dose of Seroquel taken by healthy people would likely have little effect other than making them tired.
But they warned people taking other medications or with major health problems should consult a pharmacist or doctor if they accidentally took the anti-psychotic.