Abstract Background Moderate to severe pain is frequently reported during the acute recovery phase following adult cardiac surgery. Multimodal analgesics are recommended for adult patients post cardiac surgery, but the optimal combination of multimodal analgesics is unknown. Purpose To synthesise the best available evidence about the effectiveness of multimodal analgesics on pain after adult cardiac surgery. Methods A systematic review was conducted according to the PRISMA-P statement and the published review protocol. Inclusion criteria were full-text papers or abstracts with adequate reporting, in any language, of randomised controlled trials (RCTs) in adult patients undergoing cardiac surgery that investigated the effect of multimodal postoperative analgesic regimens, compared to a control group. The highest mean level of patient self-reported pain intensity at rest, captured using a validated pain assessment tool, was the primary outcome measure. Results Of 3754 citations identified in the initial search to the 12th of December 2022, there were 1605 duplicates leaving 2149 citations for title and abstract screening, of which 2027 were irrelevant. There were 122 full-text papers assessed and 29 included in the review. Data were independently extracted by 2 reviewers in Covidence®. Participants (N = 2360), aged 59.5 + 8.2 years, were primarily male (N = 1561, 66.1%), weighing 78.1 +9.2 kilograms. Risk of bias was high and reporting quality was poor. Pain at rest reported in 18 (62%) studies was 3.5 (SD 1.2) in the control and 2.7 (SD 0.9) in the intervention groups respectively. Nurse-led versus patient-controlled analgesic administration was tested in 14 (48.3%) trials. All trials tested different analgesic combinations, none of which compared a combination of non-opioids, opioid agonist-antagonist agents, or full opioid agonists. Conclusions Poorly managed pain is associated with postoperative complications, unplanned readmissions, and the development of chronic pain. Robust RCTs are urgently needed to inform optimal combinations of multimodal analgesics to optimise patient recovery after adult cardiac surgery.Risk of Bias