Shimia 2014.

Methods	Double‐blind, randomized, placebo‐controlled. Single dose of intravenous paracetamol within the last 20 min of surgery or placebo.
Participants	Type of surgery: lumbar discectomy Paracetamol group Entered/completing: dropouts not reported; presumably 24/24 Age (mean, SD): 46.50 ± 14.07 Sex (male, %): 46.2% for both groups Placebo group Entered/completing: dropouts not reported; presumably 28/28 Age (mean, SD): 52.25 ± 11.46 Sex (male, %): 46.2% for both groups
Interventions	Paracetamol: 1 g in 100 ml normal saline. Duration of administration not stated. 100 ml normal saline. Duration of administration not stated.
Outcomes	Primary: pain on 0 to 10 VAS at 1, 6, 12, 18, 24 h after surgery Morphine dosage for the first 24 h postop Secondary: Adverse effects
Source of funding	Tabriz University of Medical Sciences
Were treatment groups comparable at baseline?	Yes: age, sex
Details of preoperative pain	Patients with preoperative treatment with narcotics, benzodiazepines, or clonidine were excluded
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomization method not described
Allocation concealment (selection bias)	Unclear risk	No information
Blinding (performance bias and detection bias) All outcomes	Unclear risk	All local anesthetic solutions and adjuvant drugs were prepared by an anesthesiologist who was not involved in the performance of the study agents, patient care, or data collection. No mention that interventions appeared identical.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Unclear if all participants completed the study
Selective reporting (reporting bias)	Unclear risk	Adverse effects assessment mentioned in methods, but article states there were no side effects related to treatment (without any detail)
Size	High risk	Fewer than 50 participants per arm of the study (24 paracetamol, 28 placebo)