This invention relates to: an indole derivative or a pharmaceutically acceptable salt thereof represented by formula (I):
1
wherein R
1
is, for example, hydrogen or C
1-5
alkyl; R
2
is, for example, hydrogen or hydroxy; R
3
is, for example, hydrogen or hydroxy; -Z- is a crosslinkage having 2 to 5 carbon atoms; m is an integer from 0 to 3; n is an integer from 0 to 10; R
4
and R
5
are, for example, fluoro or hydroxy; R
9
is, for example, hydrogen or C
1-5
alkyl; and R
10
and R
11
are bound to each other to form, for example, —O—; and a pharmaceutical composition comprising the same, particularly a drug acting on &dgr; opioid receptor.