10 participants received 4x doses each (42x + Placebo) in a crossover design. Essentially 40 participants (10 × 4) with an average p value of 0.0067.
In layman's terms, the p value represents the likelihood these results would be different if the trial was performed 100 times. In this case that likelihood is under 0.01% Anything under 0.05 is considered statistically significant.