Drew 2001.

Study characteristics
Methods	A 2‐armed (Gingko biloba and placebo), parallel‐group randomised controlled trial with 12 weeks duration of treatment and 4, 12 and 14 weeks duration of follow‐up
Participants	Location: Birmingham, UK Setting: carried out entirely by mail and telephone Sample size: Number randomised: 489 in Ginkgo biloba group and 489 in placebo group Number completed: 478 in Ginkgo biloba group and 478 in placebo group Participant baseline characteristics: Age (mean (SD) years): 52.9 (9.3) in Gingko biloba group versus 53 (9.3) in placebo group Gender (male/female, n): 338/151 in Gingko biloba group versus 338/151 in placebo group Other characteristics: average duration of tinnitus was 10 years in the intervention group and 10.1 years in the control group. Data for baseline tinnitus severity, baseline tinnitus loudness, laterality and characteristics, baseline depression and anxiety, baseline degree and characteristics of hearing loss were not provided. Inclusion criteria: participants with tinnitus Exclusion criteria: age < 18 years or > 70 years old, pregnant or trying to get pregnant, previously taken Ginkgo biloba extract, had had tinnitus for < 12 months, reported that their tinnitus had varied greatly in the 6 months before the screening questionnaire, tried any treatment for tinnitus in the 6 months before completing the screening questionnaire (for example, acupuncture, homoeopathy, hypnotherapy, etc.), not generally in good health, taking anticoagulant drugs or antidepressants, abnormal blood pressure
Interventions	Intervention group: Ginkgo biloba tablets (50 mg of Ginkgo biloba standardised extract LI 1370 containing 25% flavonoids, 3% ginkgolides and 5% bilobalides), 3 tablets daily for 12 weeks Comparator group: placebo tablets, 3 tablets daily for 12 weeks Use of additional interventions: none reported
Outcomes	Primary outcomes: change in loudness measured with a categorical rating scale (‐6 to 6) and change in troublesome nature of tinnitus measured with a categorical rating scale (‐4 to 4) at 4, 12 and 14 weeks Secondary outcomes: non‐standard questionnaire created for this study: loudness questions, awareness/ability to ignore tinnitus, impact questions, tinnitus variability, cerebral insufficiency, compliance and side effects at 4, 12 and 14 weeks
Funding sources	This work was funded by the British Tinnitus Association in conjunction with Lichtwer Pharma UK, manufacturer of the extract used in the study
Declarations of interest	The study was financed (2 years' salary for SD and running costs) by a contract between the British Tinnitus Association and Lichtwer Pharma GmbH, Berlin, who also supplied the Ginkgo biloba extract and placebo tablets
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Participants were paired according to the criteria described. Each pair was then allocated two numbers from a randomly arranged code. One number corresponded to placebo treatment and one to active treatment."
Allocation concealment (selection bias)	Low risk	Quote: "Placebo tablets were identical to the active tablets in shape, size, colour, and packaging. The tablets were dispensed in coded bottles, and treatment allocation was masked. The allocation procedure ensured that all matched participants received active or placebo tablets without the code being identified."
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "Placebo tablets were identical to the active tablets in shape, size, colour, and packaging. The tablets were dispensed in coded bottles, and treatment allocation was masked. The allocation procedure ensured that all matched participants received active or placebo tablets without the code being identified."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "Data entry and initial analyses were carried out by a researcher blinded to the participant’s allocation."
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Analyses on unmatched data were performed but not reported, except statement that: Quote: "Unmatched analyses did not provide any additional information and have therefore been excluded from this paper."
Selective reporting (reporting bias)	Low risk	All stated outcome measures reported.
Other bias	Unclear risk	Limited reporting of baseline data regarding tinnitus characteristics and severity. Participants were matched for age, sex and duration of tinnitus and stated cause of tinnitus but not severity. No data regarding ‘unmatched’ participants characteristics (i.e. was a specific group excluded from the analysis).