A recent outbreak of so-called “werewolf syndrome” among babies in Spain prompted an investigation by health officials who eventually discovered that a drug company was mislabeling its products. A total of 17 cases of unexpected hair growth in young children — a condition known as hypertrichosis — initially left doctors puzzled, but a check of a nearby pharmaceutical company’s operations revealed the cause.

As Guardian reports, drug supplier FarmaQuimica Sur was found to be accidentally mislabeling the medication minoxidil, which is the active ingredient in hair regrowth drugs like Rogaine. The drug was distributed to pharmacies as omeprazole, a drug to treat gastric discomfort.

In each of the 17 known cases, young children had been given what doctors thought was omeprazole to ease digestive issues. The children began to grow hair all over their bodies, and both parents and doctors were at a loss to explain it.

Aside from the unexpected hair growth, it’s unclear if any of the children experienced any serious side effects. Like many medications, minoxidil has its own list of possible side effects and has been known to cause heart-related issues in adults. However, Guardian reports that health officials monitoring four of the cases said the children were doing fine, and ceasing the medication is expected to reverse the hair growth.

The medication reportedly came from India, and what correctly labeled as minoxidil when it arrived in Spain. However, when the medication was processed for distribution it was labeled incorrectly and shipped out to unwitting pharmacies in Spain.

As you would expect, all of the medication has been pulled from the market and the laboratory itself has been shuttered while officials figure out how such an incredible mix-up could have happened in the first place.