I know one China virus protocol includes 10mg per day. When I was overcoming I tried a whole 3mg pill and it wiped me out about 36 hours. My wife tried 3 pills of 9 mg total and that was too much for her. She can handle 3mg though. So we do not include melatonin in our protective / recovery supplements.
I read that an effective sleeping dose is .3 mg so I take a little bite of 3 mg pill.
Similarly, I read that .3 is the amount a healthy body produces internally. I take slightly less than .25 mg and it’s effective. Any more than that leaves me groggy - and depressed if it do it for several days in a row.