Over a dozen children in Spain have been diagnosed with "werewolf syndrome" after a major medicine mix-up, media reports said.

The Spanish Agency of Medicines and Medical Devices confirmed the outbreak of hypertrichosis -- commonly known as "werewolf syndrome", to El Pais newspaper on Wednesday after 17 cases were reported by parents in three regions in Spain.

The babies began growing hair all over their body after being given what was thought to be omeprazole -- a drug that helps with gastric reflux. But later it was discovered that the treatment actually contained minoxidil -- a medication used for the treatment of hair loss, reports say.

An investigation by the agency found that one manufacturer in Spain, Farma-Química Sur, was to blame for a labelling mix up that resulted in children accidentally ingesting minoxidil, according to reports from El Pais and Granada Hoy.

Babies who were repeatedly given the incorrectly-labelled omeprazole developed hypertrichosis, causing hair to grow rapidly on their forehead, cheeks, arms and legs, according to one mother's account to El Pais.