You can indeed purchase melatonin over the counter at any vitamin store- no problem. The suggested amount is 3 mg for every 35 to 100 lbs - 3x a day. I would suggest since it's more the loud noises of the fire works freaking him out start at the beginning of the day with one and 6 hours-8 hours later another one. I wouldn't give it to him all the time for the reason of tolerance just like humans. They do sell a doggie version of it at pet stores. There are multiple brands to try. I do suggest talking to your vet about it- just ease your mind and make sure for proper dosage and more medical information. Just incase.