Effectiveness of olfactory stimulation on improving cognitive function and behavioral and psychological symptoms of dementia in older adults with mild cognitive impairment or dementia: a systematic review and meta-analysis

Objectives This systematic review and meta-analysis examined the effectiveness of olfactory stimulation on cognitive function and behavioral and psychological symptoms of dementia (BPSD) in older adults with mild cognitive impairment (MCI) or dementia.Method Following PRISMA 2020 guidelines PROSPERO (CRD42025641764), five databases were searched up to July 2025 for randomized controlled and quasi-experimental studies. Risk of bias was assessed using RoB 2.0 and ROBINS-I. Meta-analyses were conducted using Comprehensive Meta-Analysis software. Subgroup analyses examined differential effects in MCI and dementia populations.Results Ten studies met inclusion criteria, and six were included in meta-analyses. Olfactory stimulation showed a small, non-significant effect on cognitive function (Hedges’ g = 0.25, p = 0.14). Subgroup analysis revealed a moderate, marginally non-significant effect in MCI (Hedges’ g = 0.75, p = 0.08) and a small, non-significant effect in dementia (Hedges’ g = 0.16, p = 0.39). Olfactory stimulation was significantly associated with improvements in agitation symptoms (Hedges’ g = 0.73, p < 0.001) and depression (Hedges’ g = 1.81, p < 0.001) among individuals with dementia.Conclusion Olfactory stimulation may not significantly enhance cognition but suggests potential benefit in reducing neuropsychiatric symptoms among individuals with dementia, supporting its role as a non-invasive, feasible, low-cost non-pharmacological intervention.