A team of US researchers has determined that demand for prescription codeine drops in states where adult-use cannabis has been legalised.
The researchers examined Drug Enforcement Administration data that monitors the movement of controlled substances across the country.
Their findings show a 26% drop in pharmacy-level distribution of codeine in states with recreational cannabis laws on the books, a figure that climbs to 37% in states where those laws have been in place for four or more years.
Hospital-based codeine distribution showed little change, reflecting the stricter prescribing policies that hospitals typically enforce compared with pharmacies.
Unlike a recent study examining opioid consumption in states with medical cannabis programmes, the new research found minimal effect on the distribution of opioids including oxycodone, hydrocodone, and morphine.
Senior author Coleman Drake from the University of Pittsburgh's School of Public Health said: "Where previous studies have focused on more potent opioids, codeine is a weaker drug with a higher potential for addiction.
"It indicates people may be obtaining codeine from pharmacies for misuse, and that recreational cannabis laws reduce this illicit demand."
The misuse of prescription opioids contributes to thousands of overdose deaths across the US each year.
Lead author Shyam Raman from the Cornell Jeb E. Brooks School of Public Policy added: "A reduction in the misuse of opioids will save lives.
"Our research indicates that recreational cannabis laws substantially reduce distribution of codeine to pharmacies, an overlooked potential benefit to legalising recreational cannabis use."
Separately, the US Virgin Islands has approved recreational and sacramental cannabis use for adults aged 21 and over, along with plans to clear the records of eligible individuals previously convicted of simple possession.
The territory had already authorised medicinal cannabis use in 2019.
