The study found that half of people in need of pain relief being discharged from A&E needed just five opioid tablets (5mg of morphine) to last them two weeks.
But they said that the prescription varies with each type of illness or injury – patients suffering from renal colic or abdominal pain needed only eight tablets and patients with broken bones needed 24 tablets.
Presenting the research to the European Emergency Medicine Congress in Barcelona, Professor Raoul Daoust, from the University of Montreal, Canada, said: “Opioids such as morphine can be very beneficial for patients suffering acute pain, for example when they have injured their neck or broken a bone.
“However, patients are often prescribed too many opioid tablets, and that means unused tablets are available for misuse.
“On the other hand, since the opioid crisis, the tendency in the USA is to not prescribe opioids at all, leaving some patients in agonising pain.”
He added: “We found that, in general, patients consume few opioids, but this varies depending on the type of painful condition.
“Our findings make it possible to adapt the quantity of opioids we prescribe according to patient need.
“We could ask the pharmacist to also provide opioids in small portions, such as five tablets initially, because for half of the patients, that would be enough to last them for two weeks.”