L-161,982 is an EP4 (EP4 receptor) antagonist that is selective over all other members of the prostanoid receptor family (Ki values are 0.024, 0.71, 1.90, 5.10, 5.63, 6.74, 19 and 23 μM for human EP4, TP, EP3, DP, FP, IP, EP1 and EP2 receptors respectively).