Hydroxyzine

Hydroxyzine is a potent and selective histamine H1 receptor antagonist. This action is responsible for its antihistamine and sedative effects.[12][13] Hydroxyzine also has very low affinity for the muscarinic acetylcholine receptors and NMDA receptors, and in accordance, has low propensity for producing anticholinergic or hallucinatory side effects unless in high doses. In addition to its antihistamine activity, hydroxyzine has also been shown to act more weakly as an antagonist of the serotonin 5-HT2A receptor, an agonist of the dopamine D2 receptor, GABAa receptor, and the α1-adrenergic receptor, which causes relaxant and anxiolytic effects.[14][15]

Threshold is 25mg