Keogh 2003.

Study characteristics
Methods	RCT with parallel design
Participants	39 adult participants with NYHA class II or III heart failure were randomised in a double‐blind, placebo‐controlled study to 150 mg/day of oral coenzyme Q10 or placebo for 3 months 19 participants in the coenzyme Q10 group and 20 in the placebo group Adults (> 18 years)
Interventions	Intervention: oral coenzyme Q10 150 mg/day Control: placebo
Outcomes	Symptom class by NYHA and specific activities scale Exercise tolerance by a 6‐minute walk test Walk test and treadmill exercise test (modified Naughton stress test) assessment for clinical outcomes of heart failure Plasma levels of coenzyme Q10 Assessment for the clinical outcomes of heart failure including readmission, transplantation or death, serum creatinine, sodium and potassium
Notes	Study was partially funded by pharmaceutical companies that manufacture and distribute coenzyme Q10 supplements.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomised, no details about random sequence generation mentioned
Allocation concealment (selection bias)	Unclear risk	No information given
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐blind
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No information given
Incomplete outcome data (attrition bias) All outcomes	High risk	In the placebo group, 2 participants withdrew: 1 because of a rash and nausea and the other for epigastric burning with a history of peptic ulceration In the active group, 1 participant withdrew after 56 days due to increased lethargy and 1 withdrew in order to start carvedilol (prohibited medication)
Selective reporting (reporting bias)	Unclear risk	No study protocol was available.
Other bias	Low risk	No other bias could be found.