Characteristics of the seven trials from five studies
| Study, year | Study design (phase) | Intervention versus placebo: dosage (patients (n)) | Age (years)# | Female (%) | Cough duration (years)# | Diagnosis | Treatment duration | Follow-up (weeks) | Location |
| Abdulqawi et al., 2015 [15] | Crossover RCT (phase 2) | 600 mg¶ (24) Placebo (24) | 55 (24–70) | 75 | 9 (3–25) | RCC or UCC | 2 weeks | 8 | UK |
| Morice et al., 2019 [28] | Crossover RCT (phase 2) | 100 mg (24) Placebo (24) | 62±8.7 | 88 | 14.6±9.9 | RCC or UCC | Once | 2 | UK |
| Smith et al., 2020a+ [19] | Crossover RCT (phase 2) | 50/100/150/200 mg¶ (29) Placebo (29) | 63±7.4 | 86 | 15.4 (range 1.4–55.3) | RCC or UCC | 16 days | 11 | USA |
| Smith et al., 2020b+ [19] | Crossover RCT (phase 2) | 7.5/15/30/50 mg¶ (30) Placebo (30) | 60±11.1 | 80 | 13.2 (range 1.9–42.8) | RCC or UCC | 16 days | 11 | USA |
| Smith et al., 2020 [16] | Parallel-group RCT (phase 2) | 7.5 mg¶ (64) 20 mg¶ (63) 50 mg¶ (63) Placebo (63) | 60±10.5 62±9.1 59±9.2 60±10.9 | 75 76 79 75 | 13.5±10.0 14.9±13.9 12.3±8.2 17.1±13.3 | RCC or UCC | 12 weeks | 14 | UK and USA |
| McGarvey et al., 2022a§ (COUGH-1) [18] | Parallel-group RCT (phase 3) | 15 mg¶ (244) 45 mg¶ (243) Placebo (243) | 60±11.7 59±13.1 58±13.1 | 74.2 74.1 74.5 | 11.8±9.1 11.2±9.4 11.7±9.9 | RCC or UCC | 12 weeks | 52 | 17 countries |
| McGarvey et al., 2022b§ (COUGH-2) [18] | Parallel-group RCT (phase 3) | 15 mg¶ (440) 45 mg¶ (439) Placebo (435) | 59±11.4 58±12.4 58±12.6 | 74.8 74.9 74.9 | 11.9±10.7 10.9±9.9 10.7±8.8 | RCC or UCC | 24 weeks | 52 | 20 countries |
RCC: refractory chronic cough; UCC: unexplained chronic cough. #: median (interquartile range) or mean±sd, unless otherwise stated; ¶: twice daily; +: trial from the same study; §: trial from the same study.