Fantastic info, thanks! I reformatted it so it's easier to read, and the link is below for anyone who wants to see the actual chart. Lots of other good info at that site, too.
Drugs that Inhibit Thyroid Hormone
Iron supplements (even the doses found in multivitamins).
Calcium carbonate supplements
Aluminum-containing antacids (such as Maalox). (
Drugs used to decrease cholesterol levels by binding bile acids, such as colestipol (Colestid) and cholestyramine (Questran) (take four to five hours apart).
Estrogens, including those found in oral contraceptives and hormone replacement therapy. May need to increase thyroid hormone while taking estrogen. Need to monitor thyroid after withdrawal from estrogen.
Sucralfate (Carafate) (take at least two hours apart).
Drugs that Are Enhanced by Thyroid Hormone
Epinephrine (adrenaline) injections. Thyroid hormone may increase the risk of serious side effects in heart disease patients given this agent.
Warfarin (Coumadin), a blood thinner. Doses of this medication may need to be reduced if thyroid treatment is started after blood thinning treatments have begun.
Many antidepressants. In some cases, potency of both antidepressants and thyroid hormones may increase.
Drugs that Are Suppressed by Thyroid Hormone
Insulin or Insulin-Sensitizers. Diabetic patients taking thyroid hormone may need additional insulin or oral hypoglycemic drugs. Stopping or reducing thyroid hormone may increase the risk of hypoglycemia.
Digoxin. Patients with heart disease may need to increase their dosage of digoxin (Lanoxin).
Drugs that Reduce Natural Thyroid Hormone Levels and May Cause Hypothyroidism
Lithium. This drug is used in bipolar disorders and has multiple effects on thyroid hormone synthesis and secretion.
Amiodarone (Cordarone). This drug, used to treat abnormal heart rhythms, contains iodine and can induce hyper- or hypothyroidism, particularly in patients with an existing thyroid problem.
Antiseizure drugs used for epilepsy, including phenytoin and carbamazepine.
Rifampin, used for tuberculosis.
Some drugs used for cancer chemotherapy.
Large doses of selenium, a common over-the-counter supplement.
http://72.14.209.104/search?q=cache:...s&ct=clnk&cd=3
Linda
Drug interactions w/thyroid hormone 
), thus making your doctor think that you are on enough thyroid meds when in fact you may need more of them (or a T3 med thrown in). When docs go by TSH alone, the patient is often left with being under-replaced and often feeling worse than before starting treatment (because the thyroid gland reduces its output of thyroid hormone due to the thyroid meds you are taking). You should try to get your doc to run free T4 and free T3 tests to really see how much thyroid hormone your body is using.
