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Hello. Thanks for the question.
Melatonin is very safe, even in large amounts. The most we typically see, is some mild sedation. I wouldn't expect any true toxic side effects.
The carrier product and treat could also lead to some nausea/ vomiting and diarrhea. That is something to be expected if many were ingested. Those signs should resolve on their own over 1-2 days.
I hope this helps, let me know if you have any other questions.
Nope, Melatonin is a very safe supplement.