Cancer remains a major contributor to global morbidity and mortality, with an estimated 19.3 million new cases and nearly 10 million deaths reported in 2020 [1,2]. Chemotherapy is the primary treatment for cancer [3] and plays a crucial role in improving patient survival. However, it can induce a wide range of side effects, including myelosuppression, nephrotoxicity, neurotoxicity, gastrointestinal toxicity, alopecia, fatigue, and other systemic reactions [4,5]. Chemotherapy-induced gastrointestinal toxicity (CIGT) is the most commonly reported adverse effect [6]. It refers to the adverse effects on the gastrointestinal tract caused by chemotherapy drugs, manifesting as nausea, vomiting, appetite loss, oral mucositis, constipation, and diarrhea [7-9]. Previous studies have reported that nausea and vomiting affect 70% to 80% of patients [10], oral mucositis affects 40% to 75% [11], and diarrhea affects up to 80% of patients receiving chemotherapy [12]. These CIGT symptoms significantly compromise the quality of life of patients with cancer, increasing the risk of treatment nonadherence or discontinuation and even leading to death in case of severe gastrointestinal toxicity [13,14].

The current management of CIGT primarily relies on pharmacological interventions, which alleviate symptoms [5] but are hindered by their cost and often modest long-term efficacy, limiting their widespread clinical application. In recent years, complementary and alternative therapies have attracted increasing attention due to their efficacy in managing CIGT [5,15]. Aromatherapy, a type of complementary and alternative therapy, uses essential oils and other aromatic compounds derived from plants to enhance health and well-being [16]. It has empirical support for alleviating nausea, vomiting [17], oral mucositis, and constipation [18], which are key symptoms of CIGT.

Existing systematic reviews and meta-analyses have predominantly focused on aromatherapy’s effects on nausea and vomiting [17,18]. Notably, no systematic reviews have yet addressed aromatherapy’s role in managing other common CIGT symptoms, including appetite loss, oral mucositis, constipation, and diarrhea. These under-studied symptoms not only exhibit high incidence rates (comparable to nausea and vomiting in some patient cohorts [19,20]) but also share pathophysiological links with nausea and vomiting, and this co-occurrence often exacerbates patient distress and impairs treatment adherence [5]. Furthermore, critical gaps remain in understanding how aromatherapy parameters influence CIGT outcomes: variations in essential oil types (eg, peppermint, ginger, and lavender); intervention forms (eg, inhalation vs topical massage); and intervention durations (short term: <2 weeks; long term: ≥2 weeks) have not been systematically compared to determine their relative efficacy for CIGT. This lack of granularity limits the translation of existing evidence into standardized clinical practice.

Thus, this protocol aims to address these identified gaps in existing evidence: by systematically evaluating the efficacy of aromatherapy for the full spectrum of CIGT symptoms in patients with cancer and clarifying the effects of key aromatherapy parameters (essential oil types, intervention forms, and intervention durations) via subgroup analyses. By synthesizing comprehensive evidence on CIGT symptoms management and parameter-specific effects, this study will provide a foundation for developing evidence-based aromatherapy interventions and optimizing CIGT management strategies, ultimately supporting improved patient quality of life and treatment tolerance.

The primary objective of this systematic review and meta-analysis is to address the identified gaps in existing evidence regarding aromatherapy for CIGT in patients with cancer. Specifically, the study aims to achieve two core goals: (1) Systematically evaluate the efficacy of aromatherapy in alleviating the full spectrum of CIGT symptoms, including nausea, vomiting, appetite loss, oral mucositis, constipation, and diarrhea in patients with cancer, rather than focusing solely on nausea and vomiting, and (2) quantify the effects of key aromatherapy variables on CIGT outcomes through subgroup analyses, with a focus on 3 critical parameters: essential oil types (eg, peppermint, ginger, and lavender); intervention forms (eg, inhalation and topical massage); and intervention durations (eg, short term and long term). These goals will collectively clarify the clinical utility of aromatherapy for CIGT and provide parameter-specific references for clinical practice.

This study will follow the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) guidelines [21] (Checklist 1). The protocol was officially registered in PROSPERO on August 28, 2024 (CRD42024578888).

This systematic review includes comprehensive meta-analyses based on aggregated data.

Ethics approval was not required for this study because it is a systematic review and meta-analysis that uses only aggregated data from previously published randomized controlled trials and does not involve the recruitment of human participants or access to identifiable individual-level data. According to our institutional ethics policies, secondary research based solely on published and fully deidentified data is exempt from research ethics board review.

Studies comparing aromatherapy with various control conditions, including blank controls, waitlist controls, placebos, usual care, and standard treatments, will be considered.

This systematic review and meta-analysis aims to summarize current evidence on aromatherapy for CIGT and specifically fill key gaps in existing research, by clarifying aromatherapy’s effects on the full spectrum of CIGT symptoms (ie, nausea, vomiting, appetite loss, constipation, diarrhea, and oral mucositis) rather than focusing solely on nausea and vomiting. All analytical procedures will adhere to PRISMA and Cochrane Collaboration standards to ensure methodological rigor, transparency, and reproducibility. The methodological quality of included studies will be independently assessed by 2 reviewers using the RoB2 tool, and the certainty of evidence will be appraised via the GRADE approach.

To explore differential therapeutic effects, we will systematically analyze differences in essential oil types, intervention forms, and durations. Subgroup analyses will be conducted to examine potential variations associated with essential oil types (eg, ginger, peppermint, and lavender); intervention forms (eg, inhalation and topical massage); and intervention durations (eg, short term: <2 weeks; long term: ≥2 weeks) based on clinical practice. These analyses are expected to clarify how intervention parameter differences influence outcomes, addressing the lack of granularity in parameter-related evidence.

By conducting a rigorous literature search, structured data extraction, and the aforementioned quality appraisal, this review will deliver a comprehensive synthesis of existing evidence. Specifically, it will clarify aromatherapy’s overall effectiveness in managing CIGT, the consistency of its effects across different symptoms, and the clinical applicability of specific aromatherapy regimens.

Ultimately, the findings may lay 3 key foundations: first, to inform the development of evidence-based aromatherapy interventions for CIGT, thereby addressing the limitation of “nonstandardized practice” in existing research; second, to optimize supportive care for patients with cancer by reducing CIGT-related distress, improving quality of life, and enhancing treatment adherence, which directly addresses the clinical harms of CIGT highlighted in the Introduction; and third, to guide future research exploring the underlying mechanisms by which aromatherapy alleviates CIGT, thus promoting the development of mechanism-driven, more targeted interventions.

This systematic review has several methodological strengths: it adheres to PRISMA-P and Cochrane Collaboration standards to ensure rigor and transparency; 2 reviewers will independently conduct literature selection, data extraction, and bias assessment, with discrepancies resolved by consulting a third reviewer; the RoB2 tool and GRADE approach will be used to enhance the reliability of results; and subgroup analyses will explore heterogeneity related to essential oil types, intervention forms, and intervention durations.

Nonetheless, certain limitations should be acknowledged: restricting the search to English and Chinese studies may introduce language bias; heterogeneity in aromatherapy interventions (eg, oil concentration and dosage regimens) could impact pooled results; unpublished negative studies may lead to publication bias; and high methodological heterogeneity among included studies may weaken the credibility of conclusions.

Despite these limitations, the findings are expected to serve as a scientific foundation for developing standardized clinical guidelines, which will ensure the safe, effective, and evidence-based integration of aromatherapy into oncology care. Ultimately, this will enable health care professionals to select appropriate essential oils, determine optimal dosages, and apply suitable administration methods, thus improving patient outcomes and promoting high-quality, patient-centered supportive care [27]. The findings will also be disseminated through peer-reviewed publications and academic conference presentations to facilitate the translation of evidence into clinical oncology practice.

This protocol outlines a comprehensive systematic review and meta-analysis aimed at evaluating the efficacy and safety of aromatherapy for CIGT in patients with cancer. Evidence from randomized controlled trials will be synthesized to clarify the therapeutic value of aromatherapy; identify effective essential oil types, intervention forms, and intervention durations; and resolve inconsistencies in existing evidence. The anticipated results will provide an evidence-based foundation for the safe and standardized integration of aromatherapy into supportive cancer care, while guiding future research on mechanistic exploration, optimized intervention protocols, and long-term clinical evaluations.