diff --git a/changelog.d/15938.doc b/changelog.d/15938.doc
new file mode 100644
index 000000000..8d99e5f4e
--- /dev/null
+++ b/changelog.d/15938.doc
@@ -0,0 +1 @@
+Improve the documentation for the login as a user admin API.
diff --git a/docs/admin_api/user_admin_api.md b/docs/admin_api/user_admin_api.md
index 23f465e98..ac4f63509 100644
--- a/docs/admin_api/user_admin_api.md
+++ b/docs/admin_api/user_admin_api.md
@@ -732,7 +732,8 @@ POST /_synapse/admin/v1/users/<user_id>/login
 
 An optional `valid_until_ms` field can be specified in the request body as an
 integer timestamp that specifies when the token should expire. By default tokens
-do not expire.
+do not expire. Note that this API does not allow a user to login as themselves
+(to create more tokens).
 
 A response body like the following is returned: