Friend, the good news is that the soft candy is not going to be toxic as you may already know. But, because of the milk and sugar, it is common to cause vomiting or diarrhea in cats. This is not a life threatening condition to go to ER vet now. This is what you can do:
1- Do not give things like Pepto Bismol or Imodium.
2- No food or water for 6-8 hours, need to give his gastrointestinal tract time to rest. Then, offer a small amount of water followed by a diet of rice (50%) and boiled boneless chicken or ground beef (50%) until the stool is back to normal then wean him back into his regular diet.
3- Supplement with a probiotic, these are friendly bacteria that help with regularity. You can buy this over the counter in any pet store.
4- If after doing the above you do not see improvement within 24 hours I would have him checked by your family veterinarian for a hands on examination.
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