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Pet Medications: Issues to Consider When Purchasing Online or at a Retail Pharmacy

Pet Medications: Issues to Consider When Purchasing Online or at a Retail Pharmacy

Do you purchase your pet's medications from an Internet or mail-order company, or have its prescriptions filled at a community or retail pharmacy? If you purchase medications from a source other than your veterinarian, you may want to consider these issues.

Medication Substitutions

Your veterinarian has received extensive training in animal medications and is best qualified to prescribe the appropriate form of medication and at the appropriate dosage. Not all medications are safe for pets. For instance, Tylenol (in any form) should never be given to pets, as it can prove fatal. Similarly, some types of insulin are not appropriate for certain diabetic pets.

If a pharmacist suggests a substitution in medication from what is prescribed by your veterinarian, you should confirm this substitution with your veterinarian before administering the medication to your pet. Certain types of drugs that may be used interchangeably in human medicine are not appropriate or effective in animals.


Even though human medication can be used in pets, often the dosage is necessarily different. Human pharmacists are trained in human pharmacology, not veterinary pharmacology, so they may not be aware of these important differences. An example of this is thyroid medication. Dogs require a much higher dose than would be appropriate in humans. Human pharmacists who are not aware of this may try to lower the prescribed amount. This change would result in an unfavorable response to treatment by the pet. If a pharmacist suggests any change in dosage or frequency of administration of a medication, be sure to confirm this change with your veterinarian before administering the medication to your pet.

Care of Medications

To preserve their effectiveness, certain medications must be kept in a controlled environment. You can be assured that medications obtained from your veterinarian have been shipped and stored properly. In most cases, the veterinary drug manufacturer will stand behind its medication should an adverse event occur, something that may not be guaranteed if the medication is purchased from a source other than your veterinarian, such as an internet pharmacy.


Medication should not be given to your pet until it is determined to be safe—and necessary. For example, dogs with an active heartworm infection should not be given preventive heartworm medication as it can lead to a fatal reaction. Screening for the infection prior to starting the preventive is a necessity. Retail (human) pharmacies are not equipped to do this screening.

Cats and Dogs Are Different

And so are their medications. Medications specifically designed for cats or dogs are not interchangeable. For instance, canine flea medications can be fatal if given to cats. Your veterinarian will ensure that the medications you receive from them are species-appropriate.


Certain medications require monitoring and follow-up care, dosage adjustments, or continued lab tests or examinations. For that reason, and due to the unfortunate possibility of an adverse reaction, it is important to have a relationship established with your veterinarian, so that appropriate and timely care can be given.

Always Double-Check

We recommend that owners always double-check any medications against their veterinarian's orders before administering them to their pet, and to contact their veterinarian for clarification if a retail pharmacy suggests a drug substitution or a dosage change.

If you have any questions or concerns about your pet's medications, please do not hesitate to contact your veterinarian. He/she is the expert on pet medications, and is there to help you and your pet!

Ordering Safely from Online Pharmacies

After taking the above issues into account, if you decide to order from an online pharmacy, you will want to check that it is legimate. The National Association of Boards of Pharmacy manages the domain .pharmacy to ensure the legitimacy of pharmacies using that domain name. The Buying Safely section of provides a list of .pharmacy sites as well as information on spotting rogue online pharmacies.

Additionally, out-of-state pharmacies must be licensed in Oregon if they fill prescriptions for Oregon patients. You can verify that a pharmacy holds a license to dispense in Oregon through the Oregon Board of Pharmacy.

Updated: October 12, 2017