A demilich's Energy Drain ability says:
Each creature within 30 feet of the demilich must make a DC 15 Constitution saving throw. On a failed save, the creature’s hit point maximum is magically reduced by 10 (3d6). If a creature’s hit point maximum is reduced to 0 by this effect, the creature dies. A creature’s hit point maximum can be restored with the greater restoration spell or similar magic.
Does this have any effect on current hit points of targets?