Purpose: Stereotactic radiosurgery (SRS) yields excellent local control in patients with a limited number of brain metastases (BMs), but radiation-induced cerebral edema and radiation necrosis (RN) in particular may cause dose-limiting late toxicity, with the same holding true after fractionated radiation therapy for glioma. In symptomatic patients, the first-line standard of care includes corticosteroids, which may, however, be counterproductive in the evolving era of immunotherapy. Boswellic acid (BA), available as an over-the-counter dietary supplement, has been suggested as a potential corticosteroid-sparing alternative because of its anti-inflammatory and antiangiogenic effects. Methods and Materials: We performed a comprehensive literature search of the MEDLINE, Embase, Scopus, and Cochrane databases, identifying publications reporting on the use of BA during or after brain irradiation in humans. Using the Realist and Meta-Narrative Evidence Syntheses: Evolving Standards framework, relevant data are summarized using a meta-narrative approach. Results: Six records (3 for edema reduction in large irradiated volumes and 3 for RN after SRS) were identified, encompassing 130 patients. Roughly half of patients benefited from BA (radiographically or clinically) and about one third could successfully taper dexamethasone or prevent its long-term intake. Tolerability of BA was favorable, with mild gastrointestinal discomfort being reported most frequently. Current drawbacks include unknown optimal formulation as well as timing and dosing, a considerably large number of required daily capsules, and uncertain interactions with other drugs. Conclusions: Overall, the clinical evidence on the use of BA for radiation-induced cerebral edema and RN is lacking and well-designed prospective trials are warranted to further investigate this potential low-cost corticosteroid-sparing option.