CI-988 hemihydrate (PD134308) is a potent, selective and orally active CCK2R (cholecystokinin 2 receptor) antagonist with an IC 50 of 1.7 nM for mouse cortex CCK2. CI-988 hemihydrate shows >1600-fold selectivity for CCK2 over CCK1 receptor. CI-988 hemihydrate has anxiolytic and anti-tumor effects.