In general, puppies should only be given flea treatments after they're weaned—typically around seven or eight weeks of age. It's important to check the age range on the flea treatment you're using to see if it's safe to use on your puppy. Your vet will also be able to recommend an appropriate treatment for your young dog. "The pet’s size is important to consider. For instance, for our itty-bitty dogs (like teacup Chihuahuas or Yorkies) a smaller size option is necessary and for giant breed dogs, we may need to give two different sizes to make sure we are getting to a therapeutic dosage," Dr. Hall says.