Hydroxyzine pamoate is a histamine H1-receptor antagonist. Target: Histamine H1-Receptor Hydroxyzine inhibits carbachol (10 μM)-induced serotonin release by 34% at 10 μM, by 25% 1 μM and by 17% 0.1 μM in pretreated bladder slices for 60 min [1]. Hydroxyzine (0.1 mM) treatment inhibits the progression and severity of EAE by 50% and the extent of mast cell degranulation by 70% in Lewis rats with allergic encephalomyelitis (EAE) [2]. Hydroxyzine (500 M) significantly increases transport of etoposide to the serosal site in the jejunal everted sacs. Hydroxyzine significantly reduces the efflux and approximately 2.4 ug/mL of etoposide in the jejunum and ileum. Hydroxyzine (0.2 μg/mL) significantly enhances the efflux of RH123 to the lumen [3]. Hydroxyzine (500 μM) significantly decreases the steady-state etoposide concentration 2-fold, where the steady-state concentration reached about 0.055 μM/mL in Sprague-Dawley rats [3]. Hydroxyzine (12.5 mg/kg, 25 mg/kg and 50 mg/kg i.p.) shows little direct analgesic activity but markedly potentiates only the effect of morphine on the vocalization after-discharge which represents the affective component of pain in rats. Hydroxyzine (50 mg/kg i.p.) potentiates morphine on the tail-flick test, while Hydroxyzine (12.5 mg/kg i.p.) decreases morphine antinociception in rats [4].