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Levoxyl: Side Effects of Levothyroxine

Updated on February 6, 2017

Levoxyl (levothyroxine): What is it?

Levoxyl is a thyroid hormone tablet used to replace our own "home made" thyroid hormone when a patient's thyroid gland does not produce enough. Specifically, it is what we call "T4" which is the more active form of thyroid hormone we make. Levoxyl is a "synthetic" hormone and is an exact replica of the T4 naturally found in our body.

Thyroid hormone tablets are used to treat hypothyroidism. This condition effects nearly 1 in 20 adults in the U.S. Causes of hypothyroidism include things like Hashimoto's Disease (the most common reason), thyroiditis, surgical removal of the thyroid gland, certain medications (like lithium, amiodarone, sulfonamides, tolbutamide) and radiation. Common symptoms of low levels of thyroid hormone (hypothyroidism) are fatigue, weight gain, brittle fingernails or hair, constipation, puffy face, hoarse voice and depression.

Levothyroxine (T4) 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 (King Pharmaceuticals, a Pfizer Company)
  • Levothroid (by Forest Labs)
  • Synthroid (by Abbott)
  • Tirosint (by Akrimax) - the only product in a liquid gelcap that has no other fillers or color additives (it is just pure T4, gelatin, glycerin and water)
  • Unithroid (by Jerome Stevens Pharmaceuticals) - Unithroid holds the honor of being the first FDA approved levothyroxine product on the market.

Commercially available products that contain both T3 and T4(thus mimicking what our thyroid gland actually produces) are also available. These include:

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.

Levothyroxine: 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 adjusted down. However, it should be pointed out that many patients experience no side effects from levothyroxine at all.

Possible side effects of levothyroxine products are:

  • Increased appetite and weight gain
  • Fever, sweating or heat intolerance
  • Headache, insomnia, increase pulse rate or blood pressure
  • Hair loss
  • Diarrhea, vomiting or abdominal cramps
  • Difficulty breathing

I often remind patients beginning on 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.

Levothyroxine: 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.

Seizure - Seizures have been reported, though this is RARE, when initiating thyroid replacement therapy.

Overdosage - Accidental overdosage is extremely unlikely. Patients should know that most often Levoxyl and other thyroid replacement products are taken just 1 DOSE DAILY. More than 1 tablet daily is very rare. However, should a patient accidentally overdose on levothyroxine, the possible side effects could include confusion, disorientation, coma and even death.

Levothyroxine: Patient Information

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, patients should...

1. Patients with diabetes or patients taking blood thinners (like warfarin) should be prepared to monitor these conditions more closely to begin with, as thyroid hormone may affect the way your body responds to these things.

2. Ideally levothyroxine products are taken first thing in the morning, about 1/2 -1 hour before breakfast on an empty stomach. You can take it with juice or coffee or water.

3. Understand that 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.

Levothyroxine: Drug & Food Interactions

Levothyroxine can be influenced by other drugs. Food, as we mentioned above, can decrease levothyroxine absorption. Additionally, the following commonly available 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 may require an adjustment in your thyroid hormone prescription include:

  • Warfarin, blood thinners
  • Anti-diabetic medications
  • Cholestyramine
  • Estrogens and Oral Contraceptives
  • Antidepressants, SSRI's
  • Diazepam
  • Lovastatin
  • Thiazide diuretics

NOTE: The above list is not comprehensive. Also, the fact that the above drugs may have an interaction with thyroid hormone replacement does NOT mean those drugs should necessarily be stopped. In most cases, your physician just needs to be aware of these things and monitor your blood levels appropriately.


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    • lucybell21 profile image

      Bonny OBrien 5 years ago from Troy, N.Y.

      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 profile image

      Hendrika 5 years ago from Pretoria, South Africa

      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 Kinnaird W profile image

      Pamela Kinnaird W 5 years ago from Maui and Arizona

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

    • justateacher profile image

      LaDena Campbell 5 years ago from Somewhere Over The Rainbow - Near Oz...

      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 profile image

      BustedBiologist 5 years ago

      Great article. Very informative and well written!

    • pharmacist profile image

      Jason Poquette 5 years ago from Whitinsville, MA


      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!

    • pharmacist profile image

      Jason Poquette 5 years ago from Whitinsville, MA


      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 Kinnaird W profile image

      Pamela Kinnaird W 5 years ago from Maui and Arizona

      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.

    • justateacher profile image

      LaDena Campbell 5 years ago from Somewhere Over The Rainbow - Near Oz...

      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!