Is there a source for the 0.3mg, because the most sleep supplements around here I've tried seem to have at least 0.5mg, or at least 1mg. They contain a mixture of other things as well, like magnesium, leonurus cadiaca, humulus lupulus.

Melatonin only supplements mostly seem to start at around 2mg. There may be few of them at 1mg.

I can't tell if I've personally had any effects from melatonin specifically though. Sometimes I may have sleep issues and those nights, I think none of those supplements do anything.