A batch of widely prescribed painkillers has been pulled from pharmacy shelves nationally after the discovery of a drug four times its strength inside one packet, prompting concerns of potential overdoses across Australia.

A sleeve of 30mg Anamorph tablets was found inside a box of 5mg Endone tablets, according to an "urgent medicine quarantine" alert circulated internally by the Australian Department of Health’s Therapeutic Goods Administration.

A box of Endone has been found to contain a sleeve of Anamorph, which is four times stronger. Credit:Justin McManus

"The Anamorph tablets are approximately four times the Endone equivalent dose, so there is a theoretical potential for overdose, particularly if taken by an opioid naive patient," the warning, seen by the Herald, says.