Huse 2001.

Methods	Allocation: randomised. Control: placebo. Blinding: double‐blind. Arm: 2‐arm cross‐over. Centre: single. Setting and location: Pain Clinic, University Hospital, Tubingen, Germany.
Participants	Inclusion criteria: leg amputees with phantom limb pain, pain intensity score ≥ 3/10 VAS, aged 18‐75 years. Exclusion criteria: neurological or psychiatric disorders, severe illness, pregnancy, breastfeeding, morphine‐specific sensitivities. Baseline characteristics n: 12. Gender: F 2, M 10. Age: mean 51 years (range 30‐71). Number randomised: 12. Number completed: 12. Baseline pain intensity: 4.7/10 (SD 1.1).
Interventions	Morphine: target 70‐300 mg. Placebo: oral glucose tablet. Duration: 2 × 4‐week treatment periods, preceded by 4‐week treatment‐free baseline period. Each treatment phase initiated by IV test infusion (same intervention as treatment phase + metoclopramide 5 mg), and treatments separated by 1‐ to 2‐week taper and washout. Starting dose of morphine not reported, possibly calculated from IV infusion. Titration allowed. 11 participants took 70‐160 mg daily; 1 took 300 mg daily. Additional analgesics: use of all analgesic and psychotropic medication was noted in the pain diary.
Outcomes	Primary outcomes Pain intensity (2‐cm VAS transformed to 10 cm to enable comparison with other scales); measured hourly. Adverse effects; measured once or 3 times daily. At the end of each treatment period: Pain‐related Self‐assessment Scale and Self‐rating Depression Scale. Secondary outcomes Ratings of placebo and verum status. Cortical reorganisation.
Notes	Oxford Quality Score: R2, DB2, W1.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Comment: states "randomized", but method used to generate random sequence not described.
Allocation concealment (selection bias)	Low risk	Quote: "a physician who had no contact with the patients was responsible for the randomized distribution of the patients to the experimental conditions and kept the code."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "Tablets were put into exactly identical pills by the pharmacy of the hospital."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Comment: participant‐reported outcomes, participant blinded to intervention.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Comment: all followed up and 0 lost during treatment phase.
Selective reporting (reporting bias)	Low risk	Comment: all planned outcomes in the methods were reported in the results.
Size	High risk	Comment: 12 participants (n < 50).