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Levoxyl: Side Effects of Levothyroxine

Just your average apothecary (pharmacist), feet firmly planted behind the pharmacy counter, whose mortar and pestle are hitched to a star.

They go by many names, but these products all have the same active ingredient: levothyroxine.

They go by many names, but these products all have the same active ingredient: 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 be 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
  • Headaches
  • Insomnia
  • 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:

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  1. 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.
  2. 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 absorption. You can take it with juice or coffee or water.
  3. 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.
  4. 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.
  5. 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 and 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
  • Antacids

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
  • Cholestyramine
  • Estrogens and oral contraceptives
  • Antidepressants, SSRIs
  • Diazepam
  • Lovastatin
  • 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.

This content is for informational purposes only and does not substitute for formal and individualized diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed medical professional. Do not stop or alter your current course of treatment. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.


Timetraveler2 on September 27, 2019:

A new doctor just changed my husband's Thyroid med from Synthroid to Levothyroxin. He took Levothyroxin years ago but did not do well with it, yet I'm hearing this generic works much better these days. Should we be worried about this change and what problems should we look for, if any.

Christina Garvis from United States on November 17, 2018:

Thank you for this information!

Bonny OBrien from Troy, N.Y. on March 10, 2012:

One of my residants here at the home where I work had changed her meds, and she had reactions to it. I'm not sure what thyroid med she was taking tho. She was having weight issues and eating a ton more than usual. She drove us nuts.

Hendrika from Pretoria, South Africa on March 08, 2012:

Thanks for the info. I am on Eltroxin as it is called in South Africa. I experience the terrible appetite even though it is a long time that I have been taking it. If you add up all the meds I am on that can influence my appetite (Amitrypteline and Epitec) it is no wonder I am hungry ALL the time!

Pamela Dapples from Arizona. on March 08, 2012:

justateacher and pharmacist, thank you. I'll keep this all in mind. So far, so good.

LaDena Campbell from Somewhere Over The Rainbow - Near Oz... on March 08, 2012:

Pamela - I would be very careful about not taking thyroid medicine that is prescribed to you. My mom stopped and started having many, many, issues - both mental and physical. Just be careful.

BustedBiologist on March 08, 2012:

Great article. Very informative and well written!

Jason Poquette (author) from Whitinsville, MA on March 08, 2012:


Thanks for sharing your experience. In the end, if the approach you are taking puts your thyroid hormone level within a normal range, then all is good. That said, T4 and the T3/T4 combos are quite natural in my opinion. They replicate exactly what our bodies naturally make. Best wishes!

Jason Poquette (author) from Whitinsville, MA on March 08, 2012:


Thanks for reading and sharing. Taking it in the evening is fine too. More important than anything is just consistency. If your thyroid levels have been checked and everything is within normal are good!

Pamela Dapples from Arizona. on March 07, 2012:

While having an MRI two years ago, the technician questioned my thyroid medicine and asked if I take any other kinds of medicine. Then he proceeded with the MRI and happened to mention that his mother had decided to change to a generic brand of what I was on. In switching to the generic brand, his mother lost all of her hair. The next week when I was at the doctor's office, she suggested I need to double the dose of medicine I was taking. I asked her what would be the side effects if I just quit cold turkey and learned to eat better to control the whole problem. She said I might lose my hair. I weighed that against having to be worried about always getting my medicine -- especially once it was doubled in dosage. I halved the last three pills so that I took a half a pill for six days -- and then I kissed it goodbye.

I think doctors over-over-over prescribe for thyroid. What they should do is send us all down the street to the local naturopath for a good refresher on healthy eating.

LaDena Campbell from Somewhere Over The Rainbow - Near Oz... on March 07, 2012:

Great information. I have been taking levothyroxine for several years now. Many of the symptoms you mentioned are ones that I have - including the weight gain and hair loss. I usually take my medication at night, because that is a time that I can consistently remember to take it. Is there a significant difference if I don't take it in the morning?

Just curious!

Again, great info. Voted up and SHARING!

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