Participant characteristics
| Characteristics | Placebo n=47 (53%) | Ibuprofen n=42 (47%) | Difference between treatment groups p Value |
| Female sex (n (%)) | 34 (72.3) | 33 (78.6) | 0.66 |
| Age, mean (SD) | 41.4 (10.5) | 39.8 (7.1) | 0.42 |
| Body mass index (kg/m2), mean (SD) | 23.8 (2.5) | 23.3 (2.2) | 0.33 |
| Baseline pack weight (kg), mean (SD) | 10.2 (2.2) | 10.0 (2.1) | 0.62 |
| Prior marathons, median (25%–75%% IQR) | 4 (0.5–11) | 4.5 (0.25–10) | 0.86 |
| Prior ultramarathons, median (25%–75%% IQR) | 2 (1–5.5) | 3.5 (1.0–7.0) | 0.55 |
| Non-steroidal anti-inflammatory drug use prior to race, n (%) 0–-5×/month | 44 (93.6) | 36 (85.7) | 0.38 |
| 6–10×/month | 2 (4.2) | 4 (9.5) | 0.57 |
| 11–15×/month | 1 (2.1) | 0 (0) | – |
| 16–20×/month | 0 (0) | 2 (4.8) | – |
| Finishing quintile | 2.9 (1.4) | 2.5 (1.3) | 0.18 |
| Weight change (kg) | 1.1 (2.0) | 1.2 (1.5) | 0.70 |
| Number of ingested pills, median (25%–75%% IQR) | 3 (3–4) | 3 (3–4) | 0.31 |
| Creatinine baseline | 0.83 (0.1) | 0.83 (0.1) | 0.91 |