The UK's medicines watchdog is recalling a batch of a cholesterol-lowering drug after fake tablets were discovered.
Pharmacists will be able to replace the recalled drug
The Medicines and Healthcare products Regulatory Agency (MHRA), in conjunction with Pfizer, is recalling packs of Lipitor 20mg tablets.
Only those bearing the batch number 004405K1 are affected.
The MHRA said patients were not at any immediate risk from the fake drugs, which should be returned to chemists.
Patients will then be given new supplies of the prescription-only drug.
Fake tablets can be identified because they do not come in sealed packets in which the genuine drug is provided.
Pfizer said hundreds of batch numbers were released each year, and the recall only applied to this one.
There were around three million prescriptions for Lipitor issued in 2004.
Seventy-three packets of counterfeit Lipitor have so far been discovered after a tip-off from customs officers in Rotterdam, Holland.
It is the third time since the beginning of 2004 that fake drugs have entered the pharmaceutical supply chain in the UK.
Last year, counterfeit batches of Cialis, used to treat impotence, and Reductil, used to treat obesity, were discovered.
Nimo Ahmed, head of intelligence at the MHRA, said: "It is the vigilance of the MHRA that has led us to identify the counterfeit Lipitor and recall this product.
"Although the quality of counterfeit medicines cannot be guaranteed, our testing of the counterfeit product indicates that there is no immediate risk to patients. If patients have any concerns about possible side-effects they should discuss them with their doctor."
Pfizer called for more effort to be made by authorities in the UK and Europe to ensure the safety of medicines
Kate Lloyd, medical director of Pfizer UK, said: "Patient safety is our top concern and we are seriously alarmed at the discovery of counterfeit medicine in the UK.
"Patient safety is at risk if counterfeit products can easily be introduced into the supply chain through cross-border trade, as patients will not gain the benefits their doctor intended when selecting their medicine."
She said measures including outlawing the repackaging of original manufacturers' medicines, supporting the introduction of tamper-resistant medicine packaging, and introducing a standardised European barcode for medicines could all help to protect medicine supplies.
However, Richard Freudenberg, of the British Association of European Pharmaceutical Distributors, told the BBC News website it was disingenuous of Pfizer to associate counterfeits with parallel distribution.
He said overlabelling or repackaging undertaken by parallel distributors was carried out under strict guidelines.
"The impression left by Pfizer UK's medical director is that parallel distribution of medicines in Europe is thoroughly flawed and a soft target for counterfeiters to introduce their illegal and dangerous products into the market.
"In fact, there has never been a single confirmed case in the UK of a counterfeit medicine reaching a patient as parallel distribution, ever.
Mr Freudenberg said the current fakes were a replica of the pack distributed by Pfizer in the UK.
"Counterfeit medicines in Europe remain remarkably rare.
"Parallel distributors, however, are concerned about the future possibility of their entering the supply chain, and would be pleased to discuss with manufacturers available means to prevent this happening."
Professor Peter Weissberg, Medical Director of the British Heart Foundation (BHF), said: "This is not an issue that should cause any worry for patients taking Lipitor.
"We would urge any patients who have this particular batch number on their packet to follow the MHRA's advice and return the product to where they obtained it and seek a replacement of the genuine drug."