Irreversible pulpitis, which is characterised by acute and intense pain, is one of the most frequent reasons that patients attend for emergency dental care. Apart from removal of the tooth, the customary way of relieving the pain of irreversible pulpitis is by drilling into the tooth, removing the inflamed pulp (nerve) and cleaning the root canal. However, a significant number of dentists continue to prescribe antibiotics to stop the pain of irreversible pulpitis.This review updates the previous version published in 2013.To assess the effects of systemic antibiotics for irreversible pulpitis.We searched the Cochrane Oral Health Group's Trials Register (to 27 January 2016); the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2015, Issue 12); MEDLINE via Ovid (1946 to 27 January 2016); EMBASE via Ovid (1980 to 27 January 2016), ClinicalTrials.gov (to 27 January 2016) and the WHO International Clinical Trials Registry Platform (to 27 January 2016). There were no language restrictions in the searches of the electronic databases.Randomised controlled trials which compared pain relief with systemic antibiotics and analgesics, against placebo and analgesics in the acute preoperative phase of irreversible pulpitis.Two review authors screened studies and extracted data independently. We assessed the quality of the evidence of included studies using GRADEpro software. Pooling of data was not possible and a descriptive summary is presented.One trial assessed at low risk of bias, involving 40 participants was included in this update of the review. The quality of the body of evidence was rated low for the different outcomes. There was a close parallel distribution of the pain ratings in both the intervention and placebo groups over the seven-day study period. There was insufficient evidence to claim or refute a benefit for penicillin for pain intensity. There was no significant difference in the mean total number of ibuprofen tablets over the study period: 9.2 (standard deviation (SD) 6.02) in the penicillin group versus 9.6 (SD 6.34) in the placebo group; mean difference -0.40 (95% confidence interval (CI) -4.23 to 3.43; P value = 0.84). This applied equally for the mean total number of Tylenol tablets: 6.9 (SD 6.87) used in the penicillin group versus 4.45 (SD 4.82) in the placebo group; mean difference 2.45 (95% CI -1.23 to 6.13; P value = 0.19). Our secondary outcome on reporting of adverse events was not addressed in this study.This systematic review which was based on one low powered small sample trial assessed as at low risk of bias, illustrates that there is insufficient evidence to determine whether antibiotics reduce pain or not compared to not having antibiotics. The results of this review confirm the necessity for further larger sample and methodologically sound trials that can provide additional evidence as to whether antibiotics, prescribed in the preoperative phase, can affect treatment outcomes for irreversible pulpitis.