Cough tabs are rx'd for its expectorant and cough suppressive qualities. It's usually rx'd to be given every 4 hours. The active ingredients are guaifenesin and dextrometherphan. Cough tabs work by relaxing skeletal muscles. It can also have a sedative effect and, adversely, cause an increased in heart rate. Extremely rare cases of increased gastric transit time has been observed. This is, at least, with normal medication levels.
If the pet has been overdosed, of course, I'd have to recommend taking him to a vet promptly. Symptoms you might see in the event of an overdose: problems breathing, nystagmus (eyes darting side to side or up and down very quickly) and rigid muscles.
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