I agree with Ginger. Give the Vet or Poison Control a call.
I would definitely call your vet for advice, or the safest thing would be to take Buster in.
Risperidone, apparently, can be used for dogs and cats to help with behavioural problems. But it would have to be given under strict veterinary supervision. So while not necessarily toxic, the dosage may have been wrong, and the medication could cause side effects, as well as possibly being very unsuitable for your dog.
The best thing is vets advice as soon as you can.
(sorry I have only just seen your post. )