There is concern about an increase in the number of prescriptions for opiate-based medicine to children.

Otago University researchers have looked at medicines prescribed to 1.4 million children between 2010 and 2015.

The study's just been published in the journal Pediatric Drugs.

Researcher David Woods says there is particular concern over an increase in prescriptions for tramadol, which is administered via a dropper.

"That is because it has the potential for people to be imprecise with the dose which can be dangerous."

LISTEN ABOVE AS DAVID WOODS SPEAKS TO MIKE HOSKING