Phenergan, a brand name of the drug promethazine, is safe for dogs to take in many instances; however, it is imperative to determine the underlying cause of the vomiting by taking the dog to the veterinarian, according to VetInfo.com. If the dog suffers from a bowel obstruction, for example, Phenergan use would be contraindicated. Additionally, overdosing on Phenergan can be toxic for dogs.
The recommended dosage of promethazine for dogs is 1 mg per pound based on the dog's weight, but that daily dosage should be checked by a veterinarian to ensure an accurate dose is given. This medication is given via an intramuscular injection by mouth. Side effects include behavioral changes, dry mouth and sleepiness.