Sydney, Feb 25 (IANS): The number of people with chronic non-cancer pain prescribed an opioid medicine worldwide increased in the last two-and-a-half decades, say researchers.

Chronic pain unrelated to cancer includes conditions such as chronic lower back pain, osteoarthritis and rheumatoid arthritis.

The research, published in the Journal of Internal Medicin, spanned eight countries and evaluated 42 published studies that included 5,059,098 people with chronic pain conditions (other than cancer).

Two-thirds of the studies were from the US; one study was from Australia and the other studies were from the United Kingdom, Norway, India, Spain, Denmark and Canada.

"Over this period, on average around 30 per cent of people with chronic pain were prescribed an opioid medicine," said study lead author Stephanie Mathieson from the University of Sydney in Australia.

"We noted that a higher proportion of people were prescribed a strong opioid medicine such as oxycodone compared to weak opioid pain-relieving medicines," Mathieson added.

According to the researchers, in the period 1991-2015, prescribing of opioid medicines increased markedly.

In the early studies, opioid medicines were prescribed to about 20 per cent of patients experiencing chronic pain but the later studies report rates of more than 40 per cent.

According to the findings, on average over this period approximately one in three patients (30.7 per cent) were prescribed an opioid medicine.

The study found that 42 per cent of patients with chronic lower back pain were prescribed an opioid andthe average age of those prescribed an opioid medicine was 55.7 years.

In 17 studies that described the type of opioid pain relievers prescribed: 24.1 per cent were strong combination products containing opioids (eg oxycodone plus paracetamol), 18.4 per cent were strong opioids (eg oxycodone, morphine, fentanyl) and 8.5 percent were weak opioids (eg codeine, tramadol).

The study aimed to establish a baseline for how commonly opioids are prescribed for people with chronic pain conditions (other than cancer). But the authors discovered a crucial evidence gap in prescription data in countries outside of the US.

"While we have sufficient data for this purpose for the US, we have little or no data for other countries," the authors wrote.