Earlier quoted context omitted.
You'd expect the standard OTC dose to be a sensible starting point, not potentially several times more than a younger person needs
There is a rumour that the high doses are because the correct dose was under patent. I can only find that in a comment here: https://slatestarcodex.com/2018/07/10/melatonin-much-more-th... but I could have sworn it was in the main article when I first read it. (If so that makes it less likely, because the author revises his articles for correctness) That (albeit long) article is worth reading. For example, it explain…
No, the dosage is not patented. It doesn't even make sense. How would it work? "Oh, 0.5mg is patented, so let's put 1mg in the tablets and never sell 0.5mg".
I can get all kinds of dosages from the pharmacy. However, most of what they stock is "too high", probably because there's very little research/wisdom/knowledge around the supplement.