One of the teachers who tried to stop the attack "got the whole brunt of it" and was among the people taken by helicopter from the scene, officials say.
Australia has a reputation for taking on tech giants, but experts worry about the impact of its world-first social media ban on privacy and shrinking spaces for youths.
The step comes amid growing global debate between those concerned about hastiness in prescribing such medications and those who say they are lifesaving.