For my husband 0.75 mg of melatonin helps to fall asleep within 15 minutes. The problem is that (in my personal interpretation) it lowers cortisol and then he just can't get out of bed in the morning (not before noon).
For me the same amount helps with not having a cortisol peak in the middle of the night so I can sleep thru the whole night. I get up in the morning feeling refreshed and pain-free.
Why we don't take it anymore? My husband for the reason I explained above, and for me after a few times taking it (3- 4x) it stops working, and it seems to raise my uric acid as every methyl donor does.
For a while I used it like this:
1) Had problems waking up in the middle of the night
2) Took it before bed 3-4 nights in a row and stopped
Usually it adjusted my circadian rhythm for a couple of weeks. Then I repeated the above when it got disrupted again. Untill it stopped working at all and then I always try other things to avoid cortisol peaks like magnesium, sometimes calcium, or B5, B2, B6, lysine, probiotics before breakfast - trial and error. A higher dosage never helped, I think I went up to 1.5 mg.