Thyroid hormone is not for everyone, although levels do naturally decline with age or stress. The synthetic thyroid hormone, Synthroid (T4) is commonly prescribed by many physicians when thyroid tests are abnormal and in many cases doesn't seem to work as effectively as expected. Numerous patients who take their Synthroid as prescribed, with T4 levels in the "desirable therapeutic range" do not feel much significant improvement in their condition. Some even discontinue their medication and feel no significant difference. Increasing the dose of Synthroid sometimes helps, but more often the benefit is greater when either T3 (Cytomel) is added or the patient uses Armour Thyroid (or a similar generic desiccated thyroid), which contains both T3 and T4. [New England Journal Of Medicine, 1999] Many physicians are unaware of this study.
When conversion of T4 to the more active metabolite T3 is inadequate, it becomes especially important to supplement with T3. Some T3 preparations come in a slow-release formula and are taken twice daily for a more even metabolic effect. This is because T3 does not remain active as long in the body as does T4.
Thyroid hormone is a prescription drug and is supplied by drops, pills or capsules but is usually taken orally. The synthetic version is recommended by most traditional physicians. Recently, the generic brand has been proven to be as effective as the brand names, such as Synthroid.
Clinically, it is common to check the TSH (Thyroid Stimulating Hormone) level, which is a pituitary hormone. Paradoxically, the higher this level is, the lower output the thyroid has. So, if the TSH is greater than 5, it indicates deficiency in thyroid output and/or production. Some doctors measure the actual hormone (T3 and/or T4), but the TSH is a more accurate biosensitive marker for thyroid activity.
Body temperature is regulated by thyroid function, so many Holistic physicians advocate taking the patient's temperature every three hours, starting three hours after getting up, three times, for three days. The further the temperature is away from 98.6°F, the more likely the patient is to have a transient (E. Dennis Wilson Syndrome) or permanent hypothyroidism.
Heart rate is also decreased with lower thyroid, but there are many other factors such as medication, heart disease and being "over athletic" which can also cause low heart rate and I don't recommend this to diagnose low thyroid.
If one takes thyroid, a repeat TSH should be done in three to six weeks and if this level is still high, a higher dose of thyroid is prescribed. Repeat studies are done until the TSH is less than 5. In general, the higher the TSH, the more thyroid is recommended. An ill or older patient should gradually increase his dosage until the desired amount has been established. Twice yearly, the TSH should be repeated. Two blood tests can be affected by consumption of this hormone. It can influence the protime in patients in common consistently taking Coumadin (Warfarin). Also, it will lower the cholesterol and tryglycerides in most individuals.
In the past it was thought that osteoporosis may be worsened by excessive thyroid hormones. A recent study demonstrated that osteoporosis is only seen if TSH is left below 0.1 for a prolonged period of time. The goal is to reach an effective dose of hormone while keeping the TSH above 0.1. Many physicians keep the TSH at 3-5, which may not result in much clinical improvement.
On a daily basis, whether you take the hormone on an empty stomach or with food is not important, but you should not take thyroid medications with iron pills, liquid antacids or some anti-cholesterol drugs because they will interfere with absorption.
(Sources: Am J Physiol 1997 Oct;273(4 Pt 1): pp.125-32 and J Immunol 1998 Jul 15;161(2): pp.843-9)