Abraham 2003.

Study characteristics
Methods	Controlled clinical trial; DB followed by open phase, 3‐period, cross‐over; no wash‐out period; non‐involved doctor prepared drugs and order of administration  Ff‐up after 10 days of each treatment period (DB phase)
Participants	Severe phantom pain for at least 1 month despite extensive pain therapy; majority of upper and lower extremity amputations of cancer aetiology, rest due to vascular and trauma; 10 participants, 5 males; mean age in yrs (SD): 50 (14); duration of phantom pain, months: 4.8
Interventions	dextromethorphan 60 mg for 10 days, oral dextromethorphan 90 mg for 10 days, oral placebo
Outcomes	Number of participants with ≥ 50% pain relief on subjective pain intensity score 0 to 100; Feeling of well‐being from 0 to 100; Sedation score from 0 to 100; Adverse events; Dropouts/withdrawals
Notes	Limitations related to dosing and small sample size; n = 10
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described
Allocation concealment (selection bias)	Low risk	Physician not involved in study prepared batches of medications and order of administration
Blinding (performance bias and detection bias) All outcomes	Low risk	Identical capsules; outcomes assessed at the medical centre acute pain service
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Outcomes assessed at the medical centre acute pain service but not clear if blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	Complete outcome data for all
Selective reporting (reporting bias)	Unclear risk	Results in the DB phase reported in graphical form noting level of significance but without numerical results; the results for the specified outcomes in the methods section of the published study were reported, although not necessarily as our preferred outcomes
Other bias	High risk	no wash‐out period; carry‐over effect not addressed
Size of study	High risk	n = 10