Instead of add-on treatment of CRTH2 antagonists to corticosteroids, CRTH2 antagonist monotherapy significantly improved pre-bronchodilator FEV1 (MD = 0.09, 95% CI 0.04 to 0.15, P = 0.0005), FEV1% predicted (MD = 3.65, 95% CI 1.15 to 6.14, P = 0.004), and AQLQ (MD = 0.25, 95% CI 0.09 to 0.41, P = 0.002), and reduced asthma exacerbations (RR = 0.45, 95% CI 0.23 to 0.85, P = 0.01). Here, PTGDR2 is linked to asthma.