Background: Several studies have suggested that a short course of corticosteroid therapy with the standard care increases complete sore throat resolution in 24 hours, however, corticosteroids are yet to be a common prescription for acute sore throat patients. This study aimed to confirm the effectiveness and safety of adjuvant corticosteroid treatment with standard care, by investigating the treatment response and prognostic factors associated with increased symptom resolution. Methods: This retrospective study included 40 patients with acute sore throat symptoms. The degree of sore throat was checked using the manner of Numeral Rating Scale (NRS). Patients were orally or intramuscularly administered a single dose of 10 mg of dexamethasone as an adjuvant therapy with conventional treatments. Treatment response was stratified according to the degree of resolution of sore throat at 24 hours. Results: Of the 40 patients involved, 27 (67.5%) showed more than 50% reduction in NRS in 24 hours. On the contrary, 9 patients (22.5%) experienced less than 50% sore throat resolution, while 4 (10%) reported no significant pain relief. Multivariable logistic model controlling for significant covariables revealed that cough (OR, 0.02; 95% confidence interval, 0.01-0.40; p = 0.01) was an independent factor for predicting treatment response. In addition, post-hoc analysis showed a negative association between treatment response and the degree of cough (86.7% in no cough vs. 75.0% in intermittent cough vs. 47.1% in persistent cough, P = 0.023). Additionally, none of the patients experienced infection complications. Conclusions: A single-dose dexamethasone as an adjuvant therapy with standard care is an effective and safe strategy for patients presenting with acute sore throat in primary care clinics. Specifically, the efficacy of corticosteroid treatment for sore throat was higher in patients without cough.