The dose of hydrogen peroxide is small: 1 teaspoon per 5 lbs of dogs body weight, with a maximum of 3 tablespoons. There are three teaspoons per tablespoon, so the maximum dose for dogs over 45 lbs in 3 tablespoons per dose. If the H2O2 is doing its magic, your dog should be vomiting within two to five minutes of receiving the first dose.