Tuesday's fatal accident in which a motorist reportedly under the influence of "dappo" herbs killed a pedestrian on a Tokyo sidewalk was just one more sign that abuse of the quasi-legal narcotic is rising, experts say.

The incident on a bustling street near the west exit of Ikebukuro Station also injured seven people.

Witnesses told reporters that the man at the wheel was drooling and appeared exhausted. Use of dappo herbs, sometimes referred to as synthetic cannabis, is known to cause dangerous effects such as hallucinations, intoxication and euphoria.