Olfactory Training for COVID-19-related Olfactory Dysfunction: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

The coronavirus disease-2019 (COVID-19) pandemic has led to a high prevalence of olfactory dysfunction (OD), a debilitating condition that significantly impacts quality of life (QoL). While most patients recover their sense of smell, a substantial number experience persistent COVID-OD. Olfactory training (OT) has emerged as a leading, non-invasive therapeutic strategy. A systematic review and meta-analysis were conducted on evidence retrieved from Web of Science, PubMed, Scopus, CENTRAL, and Embase through June 2025 for randomized controlled trials (RCTs) evaluating OT in patients with COVID-OD. The primary outcome was the change in objective olfactory scores, and the secondary outcome was the change in QoL scores. We used STATA software to pool outcomes using standardized mean differences (SMD) with 95% confidence intervals (CI). Ten RCTs involving 628 patients were included in the analysis. Compared to the control group, OT was associated with a significant improvement in objective olfactory scores [SMD=0.30, 95% CI (0.08, 0.51), p=0.01] and QoL [SMD=-0.40, 95% CI (-0.65, -0.15), p<0.001]. The heterogeneity among studies was low for both outcomes (I²=33.69% and I²=37.47%, respectively). OT significantly improves objective olfactory function and QoL in patients with COVID-OD. Despite these positive findings, the results should be interpreted with caution due to heterogeneity in OT protocols and variability among the included studies. Future large-scale, rigorously designed RCTs with standardized OT protocols are necessary to establish definitive clinical practice guidelines.