A compound represented by formula (IA) or a pharmaceutically acceptable salt thereof, which acts relying on an orexin (OX) receptor antagonistic activity and is useful for the treatment or prevention of diseases such as sleep disorder, depression, anxiety disorder, panic disorder, schizophrenia, drug dependence, Alzheimers disease, Parkinsons disease, Huntingtons chorea, eating disorder, head ache, migraine, pain, gastrointestinal diseases, epilepsy, inflammations, immune-related diseases, endocrine-related diseases and hypertension.所表示之化合物或該醫藥上所容許之鹽,基於食慾素(OX)受體拮抗作用,係有用於對睡眠障礙、憂鬱症、焦慮症、恐慌症、精神分裂症、藥物依賴、阿爾茨海默氏症、帕金森氏症、亨廷頓氏舞蹈病、進食障礙、頭痛、偏頭痛、疼痛、胃腸道疾病、癲癇、發炎、免疫相關的疾病、內分泌相關的疾病、高血壓等之疾病之治療或預防。
