Review: intravenous and oral opioids reduce chronic non-cancer pain but are associated with high rates of constipation, nausea, and sleepiness.

Study selection and assessment: double blind, randomised controlled trials (RCTs) in any language that compared oral, transdermal, or intravenous (IV) World Health Organisation (WHO) step 3 opioids with placebo; included .10 adults/group; and reported pain intensity outcomes assessed using a visual analogue scale, a 0–10 numerical rating scale, or a 4 point categorical scale. Study quality was assessed using the 3 item Jadad scale and a 5 item validity scale.