Cochrane Oral Health Group Trials Register and the Pain, Palliative Care and Supportive Care Group Trials Register, the Cochrane Central Register of Controlled Trials, Medline and Embase.Randomised controlled trials (RCT) were included that involved patients over the age of 18 years who had presented with a single tooth with a clinical diagnosis of irreversible pulpitis.Abstracts of studies were independently assessed by two reviewers. The primary outcome was patient-reported pain (intensity/duration) and pain relief measured on a categorical scale in the preoperative phase of irreversible pulpitis. Secondary outcomes were type, dose and frequency of medication required for pain relief. Only one trial was included so pooling of data from studies was not possible and a descriptive summary is presented.One trial of 40 participants was included. There was a close parallel distribution of the pain ratings in both the intervention and placebo groups over the 7-day study period. The between-group differences in sum pain intensity differences for the penicillin group were 6.0+/-10.5, and for placebo 6.0+/-9.5 (P=0.776; differences assessed by Mann-Whitney-Wilcoxon test considered to be statistically significant at P=0.05). The sum pain percussion intensity differences for the penicillin group were 3.5+/-7.5 and placebo 2.0+/-7.0 (P=0.290). There was no significant difference in the mean total number of ibuprofen tablets (P=0.839) and acetaminophen tablets (P=0.325) taken for pain relief in either group over the study period. The administration of penicillin over placebo did not appear to significantly reduce the quantity of analgesic medication taken (P=0.05) for irreversible pulpitis.This review based on one methodologically sound but low-powered small sample trial, provides some evidence that there is no significant difference in pain relief between individuals who had untreated irreversible pulpitis who did or did not take antibiotics in addition to analgesics.