Bakhshaee 2007

Methods	Prospective, double‐blind, placebo‐controlled, cross‐over trial
Participants	30 participants with moderate to severe idiopathic subjective tinnitus 16 gabapentin, 14 placebo Inclusion criteria: 36 to 81 years continuous non‐pulsatile tinnitus duration at least 6 months total Tinnitus Questionnaire (TQ) score > 30 Exclusion criteria: active Ménière's disease signs or symptoms of intracranial disease or vestibular disorder conductive hearing loss or surgically correctable component sensorineural hearing loss of well‐known aetiology, such as noise‐induced hearing loss totally deaf or more than moderately severe loss (> 50) in at least one frequency concurrent treatment with centrally‐acting medication diabetes mellitus related to gabapentin use (impaired renal function, (planned) pregnancy, contraindications to gabapentin, metabolic or endocrine disorder) mental retardation and severe cognitive disorders
Interventions	Intervention: 900 mg gabapentin per day Control: identical placebo (opaque starch‐filled gel capsules) Duration: 4 weeks
Outcomes	Primary outcome: psychoacoustically determined tinnitus loudness and TQ score Secondary outcome: Tinnitus Severity Index score
Notes	Drawbacks: Exclusion criteria result in an intervention group not representative of the majority of tinnitus patients (patients with sensorineural hearing loss of well‐known aetiology such as noise‐induced hearing loss are excluded) Adverse events: 3% experienced dizziness
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Quote: "every participant received the same treatment sequence, therefore evaluations could be made with each participant serving as their own control" Quote: "16 participants in the study group and 14 in the control group completed the protocol" Comment: this study is described as a RCT and the results show an intervention and a placebo group. The methods section, however, describes every participant receiving the same treatment sequence and serving as their own control. This implies a cross‐over design. As it is stated clearly that everybody received the same treatment sequence we believe that no randomisation was performed
Allocation concealment (selection bias)	High risk	Quote: "every participant received same treatment sequence" Comment: a fixed sequence excludes the possibility of allocation concealment
Blinding (performance bias and detection bias) All groups	Unclear risk	Quote: "double blind" Quote: "neurontin capsules and placebo were individually enclosed in snap‐lock, opaque starch‐filled gel capsules by an investigational pharmacist" Quote: "every participant received same treatment sequence" Comment: blinding not adequately described 1) Identical pills suggests blinding of patients 2) Same treatment sequence makes blinding of study personnel and outcome assessors doubtful
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: "42 patients were noncompliant with the study instructions and one failed to complete the study due to side effects" Quote: "30 patients completed the protocol" Comment: not adequately described; 59% drop‐out is implied (not included in the analysis)
Selective reporting (reporting bias)	Unclear risk	No protocol available
Other bias	Unclear risk	No adequate baseline table to check comparability of groups Not described if groups were treated equally