Side Effects of the 4 Most Common Prescription Drugs for Dogs

While many drugs for dogs help relieve painful symptoms and conditions, they usually come with costly side effects. Consider the medication's side effects when looking for treatment.


This common anti-inflammatory is usually prescribed to treat fever, pain and inflammation. Vets prefer this drug over aspirin, as it proves to be a more effective anti-inflammatory and painkiller than aspirin.

Side effects incurred include black or bloody stools (usually indicating stomach ulcer development), vomiting and appetite loss. Rimadyl administration could also lead to heightened thirst or lack of thirst, which could provoke kidney damage. Blood loss from the drug could also develop into anemia.

Dogs that already suffer from inflammatory bowel disease, liver problems, stomach or gastrointestinal ulcers or bleeding disorders should not be prescribed Rimadyl. Your dog might also develop these health problems as side effects of Rimadyl.


This antibiotic belongs to the penicillin family and is used to fight certain strains of bacteria. It cannot fight viruses or worms, but treats abscesses, skin and bladder infections, and should be used against bacteria it is proven against. Amoxicillin is a strong protein inhibitor and should not be used on dogs with high meat diets. This would greatly decrease the dog's ability to digest protein from meat.

Amoxicillin can cause diarrhea or loose stools, particularly if it fights the bacteria in the intestines. It can also cause insulin allergic reactions, resulting in fever, swelling and rashes. Vomiting, nausea and abdominal pain can result from an amoxicillin overdose. The antibiotic should be taken with food to reduce danger of side effects.

Amoxicillin has various names and formulations. Some typically prescribed ones include Amoxi-Tabs, Robamox, Amoxi-Drops and Trimox.


This medicine is prescribed to prevent muscle spasms, vomiting and provide relief to itching and skin irritation. The drug is commonly used as a sedative and in preparation for surgery and anesthetic application. Acepromazine can be given in liquid or tablet form.

Side effects include drowsiness, constipation, urine discoloration and decrease in blood pressure. Drops in blood pressure levels could result in frequent collapsing. Acepromazine can also heighten the dog's heart rate. If the dog is prone to epileptic seizures, aceporomazine could also make those seizures worse. In some cases, the drug causes the opposite effect and the dog becomes hyperactive or aggressive, instead of sedated.

Short-nosed and flat-faced dogs are more susceptible to these side effects, particularly drops in blood pressure. Young, old or pregnant dogs should also avoid acepromazine.


This antihistamine is generally prescribed to treat and prevent allergy symptoms. It also has sedative properties and can prevent or minimize itching caused by allergies. The drug is a proven treatment against many airborne allergens and its side effects are minimal.

Diphenhydramine, the chief ingredient of Benadryl, typically causes marked drowsiness, although as more doses are administered, that effect might lessen. Other side effects are dry mouth and loose stool. Your dog might also experience appetite loss, diarrhea and vomiting, but these side effects are less common.

Many veterinary drugs benefit your dog's health but can cause unpleasant side effects. The most common include diarrhea, vomiting and appetite loss. Contact your vet if your dog develops more serious or prolonged side effects.