A Queensland coroner has warned the government to "urgently" introduce real-time prescription monitoring after a toddler died from ingesting his drug-dependent grandparents' oxycodone.

Damien*, who lived with his mother, aunt and grandparents in Cairns, was 20 months old when he died.

The forensic pathologist found enough oxycodone in Damien's blood to kill an adult. Credit:AP

Although his mother was the primary carer, it was not unusual for the child to be left, for several days at a time, in the care of his maternal grandparents, both of whom "had a known history of obtaining drugs of dependence, including oxycodone", Coroner Nerida Wilson found on Monday.

On the morning of his death, his mother had left him home with her parents and the boy's aunt, and "was in good spirits" despite a cold.