Users of Nurofen Plus have been warned to check packets after it emerged that thousands of them may contain antipsychotic drugs.
Last night's safety alert followed reports that some batches of the pain reliever contain individual blister packs of another drug, Seroquel XL – an antipsychotic drug used to treat disorders such as schizophrenia, mania and bipolar depression.
The drugs are thought to have been mistakenly inserted into batches at a wholesaler and thousands of packs could be affected. The packs have been found in pharmacies across the UK, prompting the Medicines and Healthcare Products Regulatory Agency (MHRA) to urge extra vigilance.
People who accidentally take Seroquel may experience sleepiness and are advised not to drive or operate machinery until they know how the tablets have affected them. The MHRA is advising anyone who thinks they may have taken one to contact their doctor.
The affected packs of Nurofen Plus all contain 32 tablets and are from batch numbers 13JJ, 57JJ and 49JJ. Each batch contains between 4,000 and 7,500 packs, or around half a million tablets. Not all packs are affected.
The large capsules of Seroquel XL 50mg tablets have gold and black packaging, while Nurofen Plus tablets are smaller and have silver and black packaging.
Reckitt Benckiser, manufacturer of Nurofen Plus, issued a statement saying three cases had been identified so far, all in south London. "Serious investigations" were under way to establish how the mix-up occurred, it said. Seroquel XL is manufactured by another drug firm, AstraZeneca.
"Manufacturing errors by the makers of Nurofen Plus or Seroquel XL are not thought to be part of the cause at this stage," the statement said.
"We are taking this matter very seriously and are working closely with the regulatory authority, the MHRA, and pharmacies."