Williams 2003.

Methods	Randomised crossover study
Participants	Stable heart failure Age range 38 to 75 years Mostly male (N = 15)
Interventions	Diamorphine 1 or 2 mg given intravenously Compared to intravenous saline
Outcomes	Primary outcome of breathlessness was not measured Oxygen consumption Exercise duration Respiratory rate
Notes	Naloxone 0.4 mg was given at the end of the test
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	The study authors did not clearly state the methods of random sequence generation.
Allocation concealment (selection bias)	Unclear risk	The study authors did not clearly state the methods of allocation concealment.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	The study authors did not clearly state whether they blinded participants and personnel.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	The study authors did not clearly state whether or not they performed blinding of outcome assessment.
Incomplete outcome data (attrition bias) All outcomes	Low risk	The study authors reported all follow‐up and completion data.
Selective reporting (reporting bias)	Low risk	We did not detect any selective reporting bias.
Other bias	Low risk	We judged that this trial appeared to be free of other sources of bias.
Size bias	High risk	This study had a small sample size; there were < 50 participants per treatment arm.