Table 3 Patients’ inclusion and exclusion criteria

Inclusion criteria

1. Diagnosis of postinfectious cough

2. Wind-cold invading lungs syndrome in traditional Chinese medicine Zheng

3. Cough duration of 3–6 weeks

4.Baseline cough visual analog scale of 60 mm or more

5. Aged 18 to 65 years old

6. Voluntarily provide written and informed consent

Exclusion criteria

1. Cough caused by asthma, cough variant asthma, upper airway cough syndrome, eosinophilic bronchitis, gastroesophageal reflux cough, or any other concomitant conditions

2. Patients with severe pulmonary diseases such as lung cancer, lung tuberculosis, or lung fibrosis

3. Use of an angiotensin-converting-enzyme inhibitor in the last 2 months

4. Current smokers or recent ex-smokers quitting smoking less than 3 months ago

5. Patients with temperature of 37.3 °C or above

6. FeNO > 30 ppb

7. Bronchial provocation test positive

8. Post-bronchodilator FEV₁/FVC < 0.70

9. Patients with chest X-ray abnormalities

10. Patient with severe underlying cerebral, hematological, hepatic, or renal disorders or other diseases significantly affecting the survival and prognosis, such as AIDS or cancer

11. Mental patients or legal disability

12. ALT or AST > 1.5 times of normal upper limit, urine protein >+, serum creatinine abnormality, white blood cell count < 3 × 10⁹/L or >  10 × 10⁹/L, and neutrophil granulocyte> 80%

13. Pregnancy or potential pregnancy or lactation

14. Allergic constitution or known to be allergic to any component in tested drug

15. Patients taking similar medications in the last 1 month or having participated or participating in another trial in last 3 months