Friend, overdoses of glucosamine not likely to be life-threatening. But, it can cause gastrointestinal symptoms like vomiting, diarrhea, etc. I would recommend you keep an eye on him if he develops vomiting and diarrhea this is what you can do:
1- Do not give things like Pepto Bismol or Imodium. Start him on Pepcid AC (famotidine) 10mg 1.5 tablet every 12 hours for 2-3 days. You can buy Pepcid AC over the counter in any pharmacy.
2- No food or water for 6-8 hours. Need to give his gastrointestinal tract time to rest.
3- After 6-8 hours offer a small amount of water. Wait half hour, if no vomiting, offer a small amount of rice (50%) and boiled boneless chicken or ground beef (50%) 4-6 times a day. Keep on this diet for several days then wean into regular diet.
4- If he continues to vomit after doing the above he will need to be seen by your family veterinarian for a hands on examination. Symptoms that would require an ER vet visit are pale gums, abdominal swelling, profound lethargy or restlessness, etc.
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