Can Puppy Shots Cause Them to Be Sleepy or Lethargic?

Puppy shots are important for every puppy in their first few months of life. It is recommended that puppies receive a set of four shots, beginning at eight weeks and ending by six months. Just as with humans, there are side effects of puppy shots, so it is important that you monitor your puppy closely after each shot. Sleepiness and lethargic behavior are two common reactions.

Veterinarian examining puppy
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The vaccine itself, often a 5-way shot preventing against parvo, hepatitis, lepto, distemper and parainfluenza, can cause mild reactions. Sleepiness and lethargic behavior are mild reactions, and not harmful or threatening unless the behavior lasts more than a day.

Reasons for being sleepy or lethargic

Other reasons for your puppy to be lethargic or sleepy, aside from the actual shot, can be simply from the excitement and adventure of the day. This often entails a car ride to the vet, a visit with strange people (veterinarian and techs), and strange and new places and sounds. The excitement can then cause the puppy to be sleepy afterwards.

Other mild reactions.

Other mild reactions to puppy shots can be a slight fever or decreased appetite. Simply keep an eye on your puppy and keep him comfortable during the next day or so.

More severe reactions.

More severe reactions to puppy shots can include swelling and hives, which generally occur within a few hours of receiving the vaccine. If this happens to your puppy, contact your veterinarian for advice. They may or may not require a trip to their vet, depending on severity. Anaphylaxis is the most severe reaction and can be life threatening. This occurs when the puppy has trouble breathing or standing, and will require medical attention immediately. Anaphylaxis is rare, and will occur within minutes of receiving the shot.


Despite the reactions puppies can have to the puppy shots, the shots are extremely important. These shots protect against very deadly diseases, all of which have no cure. By vaccinating your puppy, you will ensure his health, and the health of other dogs that may come into contact with yours.