Garretts family is worried about his behavior. he no longer displays affection toward them, refuses to bathe, and thinks that his neighbors dog is sending him coded messages in his cereal. garretts family takes him to a mental health practitioner, who is most likely to treat him with

The mental health practitioner is most likely to treat him with antipsychotic medication.
This type of medication is used to treat psychotic disorders which people may suffer from when they are experiencing delusions, paranoia, hallucinations, or disordered thought. Garret is probably suffering from schizophrenia, which is why he needs to take these medications so as to relieve the symptoms.