Ogawa T, Nakamura K, Yamamoto S, et al. - Researchers conducted this retrospective cohort study to clarify the time-course of olfactory recovery and the prognostic factors in postinfectious olfactory dysfunction (PIOD) patients treated with Toki-shakuyaku-san (TSS). Medical records of patients with PIOD were reviewed in this analysis. Participants in the study were patients who received TSS or a combination of TSS and zinc sulfate. The sample consisted of 82 PIOD patients with ages ranging from 16 to 79 years and the mean duration of follow-up was 14.5 months (range 3-45 months). According to multivariate analysis, younger age (< 65 years) and residual olfactory function were significantly linked to good olfactory recovery. Over time, the authors found recovery rates in patients with PIOD. Olfactory function recovery mostly occurred during the early period (≤ 6 months). However, after the first visit, the number of olfactory recovery patients increased for a long-term duration of 24 months. Residual olfactory function and younger age have been prognostic factors exactly. TSS can serve as a useful therapeutic agent for PIOD patients. Such findings provide valuable knowledge which is helpful in counseling PIOD patients.