According to a joint assessment by the European Food Safety Authority (EFSA) and the European Medicines Agency (EMA), the presence of residues of the veterinary drug phenylbutazone (also known as bute) in horsemeat is of low concern for consumers.
The assessment was requested by the European Commission and follows the discovery of beef adulterated with horsemeat and of phenylbutazone in horse carcasses illegally entering the food chain.
The EFSA and EMA experts looked at the data and concluded that there was a low likelihood of exposure to the drug in food and that toxic effects were also unlikely from the quantities present. However, they also confirmed that it is not possible to set safe levels for phenylbutazone in foods of animal origin and recommended that it should continue to be prohibited from entering the food chain.
The assessment can be found here.