Codeine consumption in Australia appears to have plunged after it was made prescription-only. 

For the first time, a new study has evaluated a national drug policy change via wastewater sampling.

Wastewater sampling shows the significant impact of removing the strong painkiller from pharmacy counters and making it a prescription-only medication in 2018. 

Researchers report a 37 per cent overall drop in codeine consumption across Australia, according to new findings from sampling published in the journal Addiction.

The experts say their samples, taken from 49 wastewater treatment plants, which cover catchment areas for 10.6 million Australians, show the dramatic effect of withdrawing the country’s most misused legal opioid from pharmacy counters.

They compared wastewater samples taken between 2016 and 2019, 18 months before and after codeine was rescheduled and low-dose formulations removed from over-the-counter (OTC).

Codeine concentrations were converted to per capita consumption estimates, revealing an immediate decrease of 37 per cent nationally after the rescheduling and between 24 per cent and 51 per cent in all states and territories.

The Therapeutic Goods Administration estimated that, prior to 2018, OTC codeine sales were responsible for more than 100 deaths each year, taking a lead from many other countries to remove codeine from pharmacy counters, given the significant medical issues associated with its use.

Lead author, University of Queensland researcher Dr Ben Tscharke, says; “less availability not only means less chance for codeine to be misused, but also changing the perception of codeine being a harmless drug. Making it prescription-only sends a clear message about how dangerous it is.”

“Codeine is typically prescribed for short-term, acute pain management but there was anecdotal evidence that many people used it as a first-line treatment and for extended periods, without consulting a doctor.”

The wastewater samples showed that regional areas decreased by a smaller margin than cities, possibly because more people in rural and regional locations obtained a script after the change, and patients in metropolitan areas had more pain alternatives to choose from, including non-medicinal treatments.

South Australia and Tasmania had the smallest decreases - averaging 25 per cent - and the Northern Territory the largest decrease of 51 per cent.

Prior to rescheduling, codeine rates of use were approximately 25 per cent higher in regional areas.

National sales of codeine during the study period were not as close to wastewater estimates, showing a combined 50 per cent decrease in total packs of codeine sold nationally (high strength 37 per cent drop and low strength 80 per cent drop).

Researchers attribute the difference to consumption delays due to stockpiling.

Similar reductions were observed in monthly calls to poison call centres, where poisonings halved after the rescheduling of codeine.

Colder climates (ACT, Victoria and Tasmania) had a greater variance between winter and summer codeine consumption before rescheduling. This may be attributed to more chronic and age-related ailments in winter, causing pain.

“Wastewater monitoring is not able to provide conclusive reasons for consumer behaviour, but it does show the effectiveness of interventions, such as codeine rescheduling,” the researchers say.