Sickle cell anemia (SCA) is a hemoglobin structural disorder based on a mutation in which the red blood cells contain the abnormal hemoglobin S (HbS) that under certain conditions become condensed and adopt a sickle shape leading to hemolysis and vaso-occlusion [1] . These pathophysiological processes give rise to a clinical entity characterized by chronic, frequently fluctuating hemolytic anemia, recurrent, severe vaso-occlusive crises, and systemic vasculopathy. It is estimated that millions of people worldwide have SCA, yet it is most prevalent in individuals of African, Mediterranean, Middle Eastern, and Indian descent. In the U.S., there are about 100,000 people living with SCA and it is more prevalent in the black community with incidence rate of SCA at 1 in every 365 births [2] .

Pain remains a complex and persistent feature of SCA, and VOCs are the leading reason for emergency department presentation and hospitalization of SCA patients [3] . People with VOCs endured severe pain—some 30% - 40% of adult SCA patients also experience chronic and acute pain conditions that make treatment a problem [4] . The precise mechanisms of SCA pain occurrence remain unclear and various factors can be involved in its development and formation. Acute pain due to vasoconstriction and tissue ischemia is, but the transition from acute to chronic pain that is mediated by inflammation, oxidative stress, and neuroplastic changes too. To accurately measure and treat these pathophysiological processes are intrinsically multi factorial, complex affairs. Over the past few decades, the way we manage acute and chronic pain in the SCA patients has changed dramatically but a few aspects remain very problematic [4] . Morphine and other opioid analgesics have been established as the gold standard for the pharmacological management of moderate to severe pain in sickle cell anemia (SCA) [5] . The ASH 2020 guidelines recommend for the management of SCA, early use of opioids in VOCs, with morphine recommended, because it is available and provides rapid onset of analgesia [5] . Although opioids can improve pain control, concerns regarding long-term opioids safety have surfaced with today’s opioid epidemic, and their applicability to the SCA population becomes an issue of debate on appropriate prescription practices. Studies have documented differing patterns of opioid prescribing for patients with SCA, suggesting under discussion of pain and potential over dosage of opioids [6] - [8] . Clinicians have to make a very fine balance regarding chronicity, opioid sensitivity, medication compliance and potential respiratory depression [7] [9] . In addition, changes in the pharmacokinetic of certain drugs used in SCA, due to hepatic and renal function modulation, and higher levels of pain tolerance and baseline opioid usage among SCA patients, make the standardization of dosing strategies difficult.

The metabolism of morphine includes many pharmacological factors that may in part influence the mortality rate in SCA [10] . Morphine is mainly metabolized in the liver through conjugation to form morphine-3-glucuronide (M3G) or morphine-6-glucuronide (M6G). M3G, produced from morphine, has no analgesic effects, and may even interfere with analgesia and cause hyperalgesia and neurotoxicity; M6G, derived from morphine, is reported to have strong analgesic effects [7] . The levels of these metabolites may rise due to compromised metabolism in hepatic disease states and hence variations in efficacy and toxicity may occur in SCA patients. In addition, pharmacogenetic factors affecting expression of cytochrome P450 enzymes and μ-opioid receptors have been linked to susceptibility to adverse effects of opioids at normal doses.

Therefore, the interaction between morphine dosing and mortality in SCA patients is an interesting area of research. According to epidemiological findings, there seems to be an increase in mortality among patients with SCA on opioid medications [8] . While opioid related mortality has been described in multiple patient populations, data on the risk of SCA patients due to disease characteristics such as ACS, OSA and PH are lacking. A literature gap on dose‐response associations between morphine use and death risk in SCA patients exists, particularly in reference to hematological and pain management, due to a paucity of evidence‐based investigations [9] . The advent of disease-modifying therapies for SCA, including hydroxyurea, L-glutamine, crizanlizumab, and voxelotor, has transformed the disease trajectory for many patients, potentially altering pain profiles and opioid requirements [7] . Hydroxyurea, the longest-established of these therapies, increases fetal hemoglobin production and reduces the frequency of VOCs by approximately 50% [10] . More recently approved agents target different aspects of SCA pathophysiology: L-glutamine enhances nicotinamide adenine dinucleotide (NAD) redox potential, crizanlizumab inhibits P-selectin-mediated cellular adhesion, and voxelotor modifies hemoglobin oxygen affinity to reduce sickling. These agents may reduce VOC frequency and severity, theoretically diminishing the need for high-dose opioid therapy [10] . However, the impact of these modern therapies on morphine dosing patterns and associated mortality risk remains inadequately characterized in contemporary cohorts.

Given the complex intersecting factors and the substantial knowledge gaps regarding safe morphine prescribing practices in SCA, this study aims to evaluate the relationship between morphine dosing and drug-related mortality in adult patients with sickle cell anemia [4] .

The systematic review process was guided by the principles outlined in the Preferred Reporting Items for Systematic Reviews and did not directly involve patients and public [11] . This review used the Patient Intervention Comparison and Outcome (PICO) framework to formulate and state the review question as follows; what is the association between daily morphine equivalent dose and all-cause mortality in adult SCA patients? We defined daily morphine equivalent dose at the standard dosing interval for morphine injections for 4 - 6 release intervals for treatment of severe pain with Diamorphine 2.5 - 5 mg/h s.c for opiod naïve and 10 - 20 mg/2 - 4 h s.c for opioid tolerant [12] .

This systematic review reveals four key findings regarding morphine dosing and drug-related mortality in sickle cell disease patients: (1) extraordinary variability exists in morphine dosing practices across healthcare institutions; (2) multiple patient factors significantly influence dose requirements; (3) morphine-related mortality is remarkably low despite frequent high-dose therapeutic use; and (4) restrictive prescribing policies have not improved safety outcomes while potentially compromising pain management.

The most striking finding is the virtual absence of morphine-related deaths in this population despite frequent high-dose opioid exposure. The standardized mortality ratio of 0.23 suggests that SCA patients have substantially lower morphine-related death risk compared to general populations receiving opioid therapy [24] . This finding challenges broad assumptions about opioid safety and suggests that population-based opioid prescribing guidelines may not appropriately account for disease-specific risk profiles.

Several factors may contribute to the low morphine-related mortality in SCA patients [13] . The medical supervision under which most patients receive morphine therapy, development of tolerance through chronic exposure to pain and medication, typically younger patient demographics, and potential protective physiological adaptations related to the underlying disease may all contribute to reduced fatal outcomes [13] [14] . Additionally, the acute nature of most morphine administration during supervised hospitalizations contrasts sharply with unsupervised chronic opioid use patterns associated with higher mortality risk in other populations.

The documented three-fold variability in morphine dosing practices highlights fundamental inconsistencies in current clinical approaches [15] . This variability cannot be explained solely by patient characteristics or disease severity, suggesting that institutional factors and provider comfort levels significantly influence prescribing patterns [18] . The lack of standardized, evidence-based guidelines specific to SCA patients contributes to this variability and may compromise optimal pain management.

The relationship between morphine dosing and clinical outcomes proved complex, challenging assumptions about dose-response relationships. The non-linear association between dose and pain control, combined with the absence of dose-related mortality risk, suggests that clinical decision-making should focus more on individual patient response and adequate pain relief rather than arbitrary dose limitations designed for other populations. An important consideration is the extent to which general opioid safety concerns apply to SCA patients [8] . Our findings suggest that extrapolating mortality risk data from other populations may be inappropriate and potentially harmful if it leads to undertreatment of legitimate pain. The evidence consistently demonstrates that morphine-related deaths are extraordinarily rare in SCA patients, even with high-dose, frequent use.

The impact of healthcare policies represents an unintended natural experiment in population-based prescribing restrictions. The evidence of increased healthcare utilization without improved safety outcomes following restrictive policies suggests that these approaches may inadvertently harm patients with legitimate medical needs while providing no measurable safety benefit.

Clinical practice implications include the need for disease-specific prescribing guidelines that acknowledge the unique safety profile of SCA patients. The incorporation of pharmacokinetic considerations, genetic factors, and personalized dosing strategies may further optimize outcomes while maintaining the excellent safety record demonstrated in this review.

Key limitations include the heterogeneous nature of included studies, potential confounding factors in observational research, and possible reporting bias regarding adverse outcomes. However, the consistency of safety findings across different study designs, geographic regions, and times strengthens confidence in the low mortality risk profile. Future research should focus on developing standardized dosing protocols while maintaining vigilance for the rare cases of serious adverse events.

The evidence supports a paradigm shift in approaching morphine therapy for SCA patients, recognizing that this population demonstrates fundamentally different risk-benefit profiles compared to other groups receiving opioid therapy [9] . Healthcare providers and policymakers should consider this evidence when developing guidelines and making clinical decisions for SCA patients experiencing pain crises.