PROBLEM TO BE SOLVED: To provide a medicament for treatment or prophylaxis of diseases such as sleep disorder, depression, anxiety disorder, panic disorder, schizophrenia, drug dependence, Alzheimers disease, Parkinsons disease, Huntingtons disease, eating disorder, cephalalgia, hemicrania, pain, digestive diseases, epilepsy, inflammation, immune-related diseases, endocrine-related diseases and hypertension, on the basis of the orexin (OX) receptor antagonist activity.SOLUTION: A medicament comprises a branched chain alkyl heteroaromatic ring derivative having orexin (OX) receptor antagonist activity and represented by the formula (Ia) or a pharmaceutically acceptable salt thereof as an active ingredient.COPYRIGHT: (C)2015,JPO&INPIT【課題】オレキシン(OX)受容体拮抗作用に基づいた、睡眠障害、うつ病、不安障害、パニック障害、統合失調症、薬物依存症、アルツハイマー病、パーキンソン病、ハンチントン舞踏病、摂食障害、頭痛、片頭痛、疼痛、消化器疾患、てんかん、炎症、免疫関連疾患、内分泌関連疾患、高血圧等の疾患の治療又は予防薬を提供すること。【解決手段】オレキシン(OX)受容体拮抗作用を有する式(Ia)で示される分岐鎖アルキルヘテロ芳香環誘導体又はその医薬上許容される塩を有効成分として含有することを特徴とする医薬。【化1】【選択図】なし