In the similar clinical studies, another oral, potent, and selective H4R antagonist ZPL3893787 has completed phase 2 clinical trials determining its safety, efficacy, and tolerability on pruritus in adult subjects with moderate to severe AD (NCT02424253) [102] and in patients with plaque psoriasis (NCT02618616) [103] in 2016 but no results for both these studies were posted on ClinicalTrials.gov. Here, HRH4 is linked to Alzheimer disease.