A glass of milk can contain a cocktail of up to 20 painkillers, antibiotics and growth hormones, scientists have shown.
Using a highly sensitive test, they found a host of chemicals used to treat illnesses in animals and people in samples of cow, goat and human breast milk.
The doses of drugs were far too small to have an effect on anyone drinking them, but the results highlight how man-made chemicals are now found throughout the food chain.
The highest quantities of medicines were found in cow’s milk.
Researchers believe some of the drugs and growth promoters were given to the cattle, or got into milk through cattle feed or contamination on the farm.
The Spanish-Moroccan team analysed 20 samples of cow’s milk bought in Spain and Morocco, along with samples of goat and breast milk.
Their breakdown, published in the Journal of Agricultural and Food Chemistry, revealed that cow’s milk contained traces of anti-inflammatory drugs niflumic acid, mefenamic acid and ketoprofen – commonly used as painkillers in animals and people.
It also contained the hormone 17-beta-estradiol, a form of the sex hormone oestrogen. The hormone was detected at three millionths of a gram in every kilogram of milk, while the highest dose of niflumic acid was less than one millionth of a gram per kilogram of milk.
However, the scientists, led by Dr Evaristo Ballesteros, from the University of Jaen in Spain, say their technique could be used to check the safety of other types of food.