Codeine-related overdoses fell by more than half at a major Brisbane hospital in the 12 months following the upscheduling of all codeine-containing products, a study shows.

Falls were even greater in products containing less than 30mg, the dose affected by the OTC ban, according to the study by researchers from the Princess Alexandra Hospital.

The researchers reviewed codeine-related presentations (deliberate self-poisonings and recreational exposures) to their hospital in the year before and after the reschedule of products containing less than 30mg of codeine in February 2018.

They found the number of codeine-related presentations was 163 before and 77 afterwards, an overall 53% drop, according to the study in the MJA.