a 2 - phenylpiperazine derivative represented by the formula or a pharmaceutically acceptable salt , hydrate , or complex thereof : wherein each of x 1 and x 3 is oxygen or two hydrogen atoms , x 2 o , nh , nch 3 , or ch 2 , n is an integer of 0 or 1 , r 1 is hydrogen or lower alkyl and r 2 is hydrogen , cyano , tetrazolyl , aminotriazolyl , mesyl , t - butoxycarbonyl , or a lower alkyl which may be optionally substituted , r 3 is hydrogen , halogen , lower alkyl or lower alkoxy , each of r 4 and r 5 is hydrogen , lower alkoxy or trifluoromethyl , and a broken line indicates a single or double bond . the derivative may be used as a tachykinin antagonist in the treatment of diseases of the digestive system , nervous system and respiratory system , inflammation , allergy , carcinoid syndrome , chronic pain , headache , crohn disease , depression and vomiting .