Acute pain is one of the most common presentations in the emergency department (ED), occurring in more than half of patient encounters [1,2]. Therefore, pain management is a fundamental and challenging component in the field of emergency medicine. There is a constant search to find an ideal agent that acts quickly and provides pain relief with minimal side effects [3,4]. Opioids are effective analgesics and are commonly used in the ED for acute pain management. Such as traumas, fractures, renal colic, burns, and abdominal pain may warrant the use of opioids [5]. Although they exert their effects in the central and peripheral nerve system to produce positive and desirable effects (analgesia, antiinflammatory properties and euphoria) [6], opioids have been associated with dose-dependent adverse effects like respiratory and central nervous system depression, nausea, vomiting, dizziness, and constipation [7].

Recent studies have found that ketamine is an effective adjunct to opioids, providing greater pain relief than morphine alone [8,9]. Ketamine alone can provide analgesia similar to that of morphine in patients with acute visceral and musculoskeletal pain, as well as for chronic painful conditions (cancer, vaso-occlusive pain crisis associated with sickle cell disease, and in patients with high opioid tolerance and/or opioid dependency) [10]. Balzer et al. conducted a meta-analysis of the effectiveness and safety of low-dose ketamine and morphine in acute pain in the ED in 2021 [11], included 8 randomized controlled trials (RCTs) [[12], [13], [14], [15], [16], [17], [18], [19]]. They found that ketamine and morphine had similar analgesic effectiveness within 60 min of administration with comparable safety profiles, suggesting that ketamine is an effective alternative analgesic for acute pain control. Although this meta-analysis further confirms the analgesic effect of ketamine, it is not exactly consistent with the conclusions of the new and high-quality RCTs [[20], [21], [22], [23], [24], [25], [26], [27]]. The effectiveness and safety of using ketamine in the ED remains unclear.

The aim of this study was to compare the effectiveness and safety of ketamine and morphine in adult patients with acute pain in ED by using a meta-analysis method. We hypothesized that, in the treatment of acute pain, the use of ketamine could improve patients' pain earlier than morphine, without increasing the occurrence of adverse events.