Akinci 2008.

Methods	Randomised clinical trial.
Participants	Country: Turkey. Number randomised: 41. Post‐randomisation drop‐outs: not stated. Revised sample size: 41. Mean age: 45 years. Females: 27 (65.9%). Inclusion criteria: ASA status I or II. Exclusion criteria: Acute cholecystitis. History of analgesic or narcotic use. Previous abdominal surgery. Hypersensitivity to study drugs. Needed conversion to open cholecystectomy. Needed postoperative drains.
Interventions	Participants were randomly assigned to 1 of 2 groups. Group 1: tramadol 100 mg IV (n = 21). Group 2: placebo (n = 20).
Outcomes	No outcomes of interest for this review were reported.
Notes	Attempts were made to contact authors in August 2013.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Computerised allocation schedule used".
Allocation concealment (selection bias)	Unclear risk	Comment: This information was not available.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "Coded syringes used". Comment: Further details were not available.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Comment: This information was not available.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: This information was not available.
Selective reporting (reporting bias)	High risk	Comment: Mortality and morbidity were not reported.
For‐profit bias	Unclear risk	Comment: This information was not available.