Cats that take too much amoxicillin will develop symptoms such as vomiting, lack of energy, and lethargy. When giving amoxicillin to cats, owners should control the dosage according to the cat’s weight, or take the cat to a professional pet hospital for medical treatment. Take medication under your doctor's advice to avoid discomfort. Amoxicillin is a drug for humans. Try not to give it to cats. It is best to go to a pharmacy to buy medicine specifically for pets.