Melatonin can elicit negative and/or paradoxical effects. User dependant.
Thank you. I wish people would not instantly shout, "it does nothing!" as most have not done what it takes to effectively evaluate this compoud. In the 21 years I have been in supplements nothing has proven as tricky as melatonin.
Some need to take it hours before sleep when the sun starts to set.
Some need very very little ex. 250MCG
Some need to take it immediately before bed.
Some need to take a time-released while others seem to do better with sublingual and it depends on what you have more of an issue with falling vs staying asleep.
As you stated there can be a paradoxical effect if too much is taken and IMO 3mg(the standard dose in most supplements) is too much for many.
I personally like to take 500mcg after waking to pee about 2-3 hours into my sleep.
Most people do not try all of the above variables. They buy a 3mg capsule, take it a few times expecting nature's ambien and then decree it as worthless. There is also a chance one already produces more than enough naturally and in that case, there should be no sleep effect.
That being said sleep is one of the hardest things to remedy as what works well for one person seems useless for the next. IME what works well today may not a month from now. I tell people to try to find a few things that help and rotate, this is of course in addition to proper sleep hygene.