British supermarket chain Asda on Tuesday recalled all of its budget corned beef range after veterinary drug phenylbutazone was found in some samples.
The product was withdrawn last month after traces of horse DNA were discovered, and further analysis revealed the presence of "bute" at the level of four parts per billion (4ppb).
It is the first time bute has been found in a meat sample, according to the Food Standards Agency, and no other Asda products are thought to be affected.
The FSA assured customers that the chances of anyone falling ill after eating such meat were minimal.
"Horse meat containing phenylbutazone presents a very low risk to human health," said Chief Medical Officer Professor Dame Sazone.
"Phenylbutazone, known as bute, is a commonly used medicine in horses. It is also prescribed to some patients who are suffering from a severe form of arthritis," she added.
Millions of ready meals have been pulled from supermarket shelves across Europe after tests revealed that meat labelled as beef actually contained large quantities of horsemeat.