FWIW I have had no problems with the inexpensive Spring Valley melatonin. Natrol melatonin was OK. I did have problems with some of the other brands, including worsened tinnitus.
When I use it I use Spring Valley, cheapest Wal-Mart carries. I have half a bottle that I have used on and off.
Yesterday the ringing was maddening, took a melatonin last night and the ringing seems to have lessened a bit to just annoying.
I’ll see how it goes.
Thanks.