Yamagami 1986.

Methods	Randomized, placebo‐controlled, double blind trial. Washout period of 4 weeks or more with stable baseline BP. Measurement every 2 weeks for 12 weeks.
Participants	52 patients with essential hypertension (BP > 150/90 mm Hg) were selected at random from the outpatient clinic of The Center for Adult Diseases in Osaka, Japan. 20 patients (8 men and 12 women, mean age 60 years) with low CoQ10 and low SDH‐Q reductase activity were accepted. Conventional hypertension therapies were continued without change.
Interventions	Intervention: Monotherapy with 33.3 mg CoQ10 3x daily (100 mg/day) Control: Placebo
Outcomes	SBP and DBP at 2 week intervals (no description of position of patient or method of BP measurement).
Notes	Sources of funding not stated. Limited to patients with low CoQ10 levels, who could be particularly responsive to BP lowering effect of intervention.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "A total of 20 patients was randomized..." Does not describe the sequence generation process.
Allocation concealment (selection bias)	Unclear risk	"The capsules were numbered and the code was kept... until all trial had been over." Not clear whether numbers were random or in sequence.
Blinding (performance bias and detection bias) Blood Pressure	Unclear risk	Quote [direct quotation, note typographical errors]: "The capsules were numbered and the code was kept... until all trial had been over... After all data were fixed in each case, key code was opened and the change of blood pressure was compared between coQ group and placebo group." Comment: insufficient information about how key codes were assigned.
Incomplete outcome data (attrition bias) Blood Pressure	Low risk	No missing outcome data.
Selective reporting (reporting bias)	Low risk	BP data at all time points was provided.
Other bias	Low risk	SD data is as would be expected.