| 
      
        | Item | Clonidine group (n=120) | Dextromethorphan group (n=120) | Placebo 
          group (n=120) | P-value |  
        | Cough appearance, n (%) | 18 (15.0) | 14 (11.7) | 41 (34.2) | < 0.001 |  
        | Cough severity, n (%) |  |  |  | < 0.001 |  
        | Mild | 8 (6.7) | 8 (6.7) | 13 (10.8) |  |  
        | Moderate | 6 (5.0) | 6 (5.0) | 18 (15.0) |  |  
        | Severe | 4 (3.3) | 0 (0.0) | 10 (8.3) |  |  |