I also think that the health risks of taking melatonin long-term

I strongly disagree, but I also dislike plowing through as enormous a literature as that on melatonin and effectively conducting a meta-study, since Wikipedia already covers the topic and I wouldn't get a top-level article out of such an effort, just some edits for the article (and old articles get few hits, comments, or votes, if my comments are anything to go by).