Many people are unaware that most human medications are not suitable for pets. One problem is the different size of pets. An average cat weighs 5kg and an average person may weigh 70kg. So if you give a cat a human tablet you are overdosing it 14 times. Even a 30kg kelpie would be getting twice as much medication as would normally be prescribed. The second and often more serious problem is that pets may metabolise the medication differently to humans. This is particularly true of cats who lack a specific enzyme that is responsible for breaking down medications (and some potential poisons) into safer chemicals.