Cekkayan 1996.

Study characteristics
Methods	A 3‐armed (betahistine, Gingko biloba and placebo), parallel‐group randomised controlled trial with 3 months duration of treatment and 3 months duration of follow‐up
Participants	Location: Malatya, Turkey Setting: single‐centre study, Department of Otorhinolaryngology, Inönü University, from September 1993 to April 1994 Sample size: Number randomised: 26 in Ginkgo biloba group and 13 in placebo group Number completed: 26 in Ginkgo biloba group and unclear how many (8 or 13) in placebo group Participant baseline characteristics: Age (mean (range) years): 38.8 (14 to 63) in Gingko biloba group versus 50 (26 to 70) in placebo group Gender (male/female, n): 14/12 in Gingko biloba group versus 4/9 in placebo group Other characteristics: group data for degree of hearing loss are not available. Participants had degrees of uni‐ or bilateral sensorineural hearing loss varying from mild to profound. Group data for tinnitus laterality are not available. Participants with bilateral and unilateral tinnitus were included. Data for baseline tinnitus severity, duration tinnitus, baseline tinnitus loudness and characteristics, baseline depression and anxiety were not provided. Inclusion criteria: patients with subjective tinnitus Exclusion criteria: none
Interventions	Intervention group: Ginkgo biloba tablets (9.6 mg ginkgo glycoside/tablet; Tebokan Fort tbl./Rökan/Tebonin), 1 tablet 3 times a day, 3 months Comparator group: placebo capsules, 1 capsule 3 times a day, 3 months Use of additional interventions: none reported
Outcomes	Primary outcome: change in tinnitus severity scale (range of 0 to 4) at 3 months Secondary outcome: adverse effects at 3 months
Funding sources	No information provided
Declarations of interest	No information provided
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	The authors stated that participants were randomly allocated to groups but did not provide any details on methods Quote: "Randomised groups were created (...)"
Allocation concealment (selection bias)	Unclear risk	Information not reported in the manuscript.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Information not reported in the manuscript.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Information not reported in the manuscript.
Incomplete outcome data (attrition bias) All outcomes	High risk	Data on changes in tinnitus severity categories are reported only for 8 out of 13 participants (Table 3) but dropout and reasons are not mentioned. It seems that data for 5 participants in the placebo group are missing.
Selective reporting (reporting bias)	High risk	Routine and audiological examinations were performed every 15 days, however those data are not reported. Only data regarding tinnitus severity categories are reported at 3 months.
Other bias	Unclear risk	No prospective protocol available. No funding sources and declarations of interest reported. Statistical tests not reported ‐ not clear whether they were appropriate.