There are many different strengths of thyroid pills available. Dogs from four pound chihuahuas to two hundred pound mastiffs all take thyroid medication. Some pills might be, for example, 1 miligram, while other pills might be 100 miligrams. The dosage can be raised or lowered in tiny increments, until the right dosage is found. I have probably 20 customers whose dogs are on thyroid medication, and they all take different strength pills ... some take 1 pill, some 2 1/2 pills, some 1/2 of a pill in the morning and 1/4 of a pill at night. If you have a good vet, the correct dosage CAN be found to manage the thyroid condition.

However .. I have to agree with Aly ... I've never heard of thyroid imbalance causing aggression. Mostly, the problems associated with thyroid problems are excessive weight gain or loss, and problems with the coat. I know a lot of dogs with thyroid problems, and none of them were ever aggresive. If I were you, I would look into seeing a behaviorst, professional trainer and/or a new vet.