In my experience, for insomnia,
1) Melatonin, or one of its precursors, 100 mg of 5-HTP, or 600 mg of L-Tryptophan, did work for me.
However, after the first night, it stopped working for me.
But, whenever I took a higher dose, I experienced hypersomnia.
Further, L-Tryptophan never worked for me, if I took it with food.
2) GABA worked for me a bit better than Melatonin.
The dose of 500 mg was perfect for me,
and never gave me any negative side effects.
However, after 2 days, it stopped working for me.
Further, it failed to work for me, if I took it with food.
I hope this will help somebody!