Pain control is one of the major aspects in dental practice. Dental pain can usually be controlled using different techniques such as local anesthesia and medications. Acetaminophen is a pain reliever and fever reducer. However, it shows no effect on inflammation. Therefore, non-steroidal anti-inflammatory drugs are currently used to control inflammation and pain. This study sought to compare the efficacy of premedication with ibuprofen, gelofen and acetaminophen in the depth of anesthesia in mandibular molars with irreversible pulpitis. In this double-blind randomized controlled trial, 60 patients with at least one mandibular molar with symptoms of irreversible pulpitis requiring root canal therapy were recruited. Another tooth in the same quadrant was selected as the control. Patients were randomly allocated to one of the following groups: ibuprofen 400 mg, gelophen 400 mg, acetaminophen 325 mg, and placebo 500 mg. The medications were taken 30 min prior to local anesthesia and the cold test and electric pulp test (EPT) were repeated for the test teeth and the control teeth after 10 min with the development symptoms of anesthesia. Access preparation was then initiated and the patients were asked to quantify the level of pain during exposure of the dentin and pulp using a visual analogue scale (VAS). Data was analyzed using analysis of variance (ANOVA), and repeated measure ANOVA, P < 0.05 were deemed significant. There were significant differences between the mean baseline VAS score, and the mean VAS score recorded at the time of dentin and pulp exposure however revealed a significant difference in the VAS score only at the time of dentin exposure among the study groups (P < 0.005). No significant difference was observed in the mean VAS score at the time of pulp exposure among groups (P = 0.076). The EPT was significantly higher after the test compared with the baseline (P = 0.421). Premedication with ibuprofen and gelofen have significant effect in the depth of anesthesia in mandibular molars with irreversible pulpitis, and significantly decreased VAS but placebo and acetaminophen are functionally alike and had no significant effect.