Levoxyl: Side Effects of Levothyroxine
Levoxyl (levothyroxine): What Is it?
Levothyroxine is a synthetic thyroid hormone tablet used to replace the most active form of thyroid hormone (T4) that your body produces when your thyroid gland does not produce enough.
Thyroid hormone tablets are used to treat hypothyroidism. This condition affects nearly 1 in 20 adults in the U.S. Causes of hypothyroidism include Hashimoto's Disease (the most common reason), thyroiditis, surgical removal of the thyroid gland, certain medications (e.g. lithium, amiodarone, sulfonamides, tolbutamide), and radiation. Common symptoms are fatigue, weight gain, brittle fingernails or hair, constipation, puffy face, hoarse voice, and depression.
Levothyroxine is manufactured by a variety of companies in the U.S. The manufacturer often gives their product a unique name even though they have the same ingredients. Some examples of levothyroxine products currently available include:
- Levoxyl (by King Pharmaceuticals, a Pfizer Company)
- Levothroid (by Forest Labs)
- Synthroid (by Abbott)
- Tirosint (by Akrimax)—The only product in a liquid gel cap that has no other fillers or color additives (it is just pure T4, gelatin, glycerin, and water)
- Unithroid (by Jerome Stevens Pharmaceuticals)—It holds the honor of being the first FDA approved levothyroxine product on the market.
Commercially available products that contain both T3 and T4, thus, fully mimicking what our thyroid gland produces, are also available. These include:
- Armour Thyroid (by Forest Labs)—naturally derived from porcine (pig) sources
- Westhroid (by RLC Labs)
- Nature Thyroid (by RLC Labs)
- NP Thyroid (Acella Pharmaceuticals)
Since the focus of this article is to provide you with a list of levothyroxine side effects, I am not going to go into the debate about using a pure T4 product vs. using a T3/T4 combination product right now.
Common Side Effects
Patients taking thyroid replacement hormones may experience some side effects, particularly toward the beginning of therapy when the dosage may still need to be adjusted. Sometimes these side effects indicate that the dosage needs to reduced. However, it should be pointed out that many patients experience no side effects from levothyroxine at all.
Possible side effects of levothyroxine are:
- Increased appetite and weight gain
- Fever, sweating, or heat intolerance
- Increased pulse rate or blood pressure
- Hair loss
- Diarrhea, vomiting or abdominal cramps
- Difficulty breathing
I often remind patients new to levothyroxine therapy that hair loss (a bit more than normal) is not unusual at the beginning. But, typically, this ends after the first few months.
Rare Side Effects
Most side effects associated with Levoxyl or levothyroxine products are mild and reversible once the dose has been properly adjusted. There are a couple of very rare, but theoretically possible, side effects:
- Seizures: Seizures have been reported—though rare—when initiating thyroid replacement therapy.
- Confusion, disorientation, coma, and even death: Accidentally overdosing is extremely unlikely. Patients should know that most often, Levoxyl and other thyroid replacement products are taken just once daily. More than one tablet a day is very rare. However, should a patient accidentally overdose on levothyroxine, these are the possible side effects.
Information for Patients
The following are a few pieces of information I typically provide to my patients when I know they are getting a prescription for levothyroxine for the first time. In addition to the side effects of levothyroxine products, you should know:
- If you are diabetic or are taking blood thinners, like warfarin, you should be prepared to monitor these conditions more closely in the beginning as thyroid hormone may affect the way your body responds to these conditions.
- Ideally, levothyroxine products are taken first thing in the morning, about 1/2-1 hour before breakfast, on an empty stomach as food can decrease the absorption. You can take it with juice or coffee or water.
- Typically, once begun, you will be taking this medication daily for life. Therefore, it is best to establish a routine of taking it and remember to get it refilled regularly.
- It may take a few weeks for symptoms associated with hypothyroidism to resolve. Be patient. Also, be sure to let your doctor know if you experience any of the side effects mentioned above.
- Brand name levothyroxine products like Synthroid are not more effective than generically available products. However, ideally, you should stick with the same levothyroxine product from month to month. If cost becomes a concern, talk to your doctor about using a generic levothyroxine product.
Drug & Food Interactions
Levothyroxine can interact with other drugs. Food, as we mentioned above, can decrease absorption. Additionally, the following commonly used over-the-counter (OTC) medications should not be used within 4 hours of levothyroxine:
- Calcium supplements
- Iron supplements
Other prescription medications that may need to be adjusted or that may require an adjustment in your thyroid hormone prescription include:
- Warfarin and other blood thinners
- Anti-diabetic medications
- Estrogens and oral contraceptives
- Antidepressants, SSRI's
- Thiazide diuretics
Note: The list above is not comprehensive. Also, the fact that the drugs listed may have an interaction with thyroid hormone replacement does not necessarily mean those drugs should be stopped. In most cases, your physician just needs to be aware of these things and monitor your blood levels appropriately.