Synthetic forms of the thyroid hormone T4 are generally called levothyroxine, and they are considered the standard treatment for hypothyroidism. Though they are man-made, synthetic T4 hormones are exactly the same as the T4 that is produced and released by the thyroid gland.
Synthroid is the most commonly-prescribed brand of T4 for hypothyroidism. It delivers a steady, prolonged dose of T4. There is also a generic form of T4 available, which is more cost-effective than brand-name medications. Fortunately, it's also equally as effective. Synthroid (levothyroxine) is a replacement for a hormone normally produced by your thyroid gland to regulate the body's energy and metabolism. Levothyroxine is given when the thyroid does not produce enough of this hormone on its own.
All the approved brands of T4 are bio equivalent. In other words, there is no significant difference in their composition. However, that does not mean that these brands are exactly the same. The bio availability of a given brand at a given time after ingestion might be different. That's why much of the endocrinology community—the American Association of Clinical Endocrinologists, The Endocrine Society, and the American Thyroid Association—believe that once you start with a brand, you should stick with it. If you change brands during treatment, you risk altering your hormone levels. That means your symptoms may return and you may need to adjust your dose. Changing brands may change the dose slightly, which in turn may change how you feel. Thyroid hormone controls the rate of metabolism. When the thyroid is under active, all body processes slow down and symptoms such as weight gain, fatigue, and decreased body temperature are experienced. Through supplementation of thyroid hormones, basal metabolic rate will be increased.
Thyroid hormones are essential to proper development of all cells in body. These hormones allow for the body to become more sensitive to all other hormones, in turn making them more effective. Thyroid hormones also regulate macronutrient (protein, fat and carbohydrate) metabolism, therefore increasing protein synthesis and ultimately energy. This allows for the body to burn more calories and use them more sufficiently. For this reason, thyroid hormones are commonly used as fat-loss drugs.
This medicine does not typically cause side effects as long as proper dosages are administered. However some drawbacks of Thyroid drug use are cardiac stress and possible loss of lean body mass. Negative feedback in the thyroid can decrease natural production of thyroid hormone, causing short term decrease of metabolic rate after use is discontinued.
Finding your ideal T4 dosage is essential. The right dosage keeps hypothyroidism from interfering with your life. The wrong dosage can make it an even bigger problem than it was before you sought treatment.
Getting the right dosage is important, but don't expect the dosage you start out with to be the dosage that you eventually keep. Doctors often use weight as a guideline for determining dosage. Some use the formula of 1.6 micrograms of T4 for every 1 kilogram (or 2.2 pounds) of weight for a starting dosage. Others prefer a more conservative approach, starting patients at a very low dose (perhaps as low as 25 micrograms). Note the 1.6 micrograms is a full replacement dose. This means that if part of your thyroid still functions properly, you won't need this full dose because you will continue to make some of their own T4, in addition to the dose in the pill.
Because it's common for dosages to change at the start of treatment, your doctor will likely monitor your thyroid stimulating hormone (TSH) levels after two or three months (though some doctors check as soon as four weeks) from your first day of treatment. And since hormone replacement therapy is usually a lifelong treatment, you should get checked every year to make sure you're taking the right dose if you're on a stable dose. You should communicate with your doctor more frequently if your dose is being adjusted.
Doctors often err on the side of caution when prescribing starting dosages of T4 for a variety of reasons. For one, starting at a low dose and moving up lets your heart get used to the increased metabolism. Also, they don't want to induce hyperthyroidism—a condition caused by high levels of thyroid hormones. You can learn more about the symptoms of over-treatment below.
Even with a moderate dose of T4, some patients are susceptible to over-treatment symptoms. Elderly patients with weaker hearts and people with heart arrhythmias (irregular heartbeat) are especially sensitive to thyroid hormone. Generally, doctors like to start a slightly lower dose in these patients, in order not to cause or worsen irregular heart beats.
Be aware that when and how you take medication does influence its effectiveness. For example, thyroid medication should not be taken with calcium or iron. Both of these minerals bind with thyroid hormone and make it unavailable for your body's use.
Thus, you should avoid milk products two hours before and after taking thyroid medication. There are also some medications that alter T4 levels.
Aspirin, danazol and propanolol have been shown to increase T4 levels and furosemide, methadone, lithium, aluminum-containing antacids, colestipol, and rifampicin have been shown to decrease T4 levels.
There are also some unique interactions. Progesterone and estrogen are substances that can bind with T4, but also tend to increase T3 levels. Anabolic steroids tend to decrease thyroid hormone levels. Finally, thyroid hormone can suppress insulin, an important consideration for diabetics and bodybuilders using insulin.
Finally, if diagnosed with hypothyroidism, you will be taking medication for the rest of your life.
Below are some of the symptoms of over-treatment:
Feeling hot and sweating more than normal
Shaking (hand tremors)
Having difficulty falling asleep
Having mood swings
Experiencing mental "fuzziness" (forgetfulness, loss of concentration)
Experiencing muscle weakness
If you experience any of these symptoms throughout the duration of your hypothyroidism treatment, talk to your doctor immediately. He or she will first check your blood tests, before deciding on a dose.