Mansfield 1996.

Methods	Study design: parallel‐group randomized controlled trial Sample size: 66 Country: UK Setting: secondary care hospital Dates conducted: not reported Postoperative opioid used and delivery: PCA morphine Pain score collection: not reported Concurrent postoperative analgesics: none reported in first 24 hours
Participants	Inclusion criteria Females undergoing total abdominal hysterectomy with or without salpingo‐oopherectomy ASA 1 or 2 Aged 18 to 70 years Weighing 45 kg to 100 kg Exclusion criteria If individual requested exclusion Organ dysfunction Chronic pain Regular opioids NSAIDs Drug/alcohol abuse Psychiatric disorder
Interventions	Group Pre‐low (22 participants): intravenous morphine 0.15 mg/kg given during induction and placebo at peritoneal closure Group Pre‐high (20 participants): intravenous morphine 0.3 mg/kg given during induction and placebo at peritoneal closure Group Post (18 participants): placebo at induction and 0.15 mg/kg at peritoneal closure
Outcomes	Postoperative pain (1, 2, 4, 24, and 48 hours on 0‐to‐100‐millimetre VAS and 0‐to‐8 VRS at rest and movement) Morphine consumption (mg at 24 and 48 hours) Nausea, vomiting, and antiemetic requirement (all yes/no at 24 hours)
Notes	Funding: not reported Declarations of interest: not reported Authors contacted: we contacted authors for further information but received no response. Other: results reported as median so included in narrative synthesis. Pain data extracted from graph using computer software.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No details
Allocation concealment (selection bias)	Low risk	Pharmacy controlled. Quote: "pharmacy prepared 10ml colourless solutions which were sequentially numbered"
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐dummy used. Quote: "pharmacy prepared 10ml colourless solutions which were sequentially numbered"
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Blinded based on above information. Quote: "all investigators were blinded to the contents of the pair of ampoules"
Incomplete outcome data (attrition bias) All outcomes	Low risk	Dropouts unlikely to bias results. 1 participant from 1 group excluded due to severe anxiety, but number too small to affect results.
Selective reporting (reporting bias)	Unclear risk	No protocol or trial registration
Other bias	Low risk	Similar baseline characteristics