Levothyroxine Side Effects

Heart palpitations, difficulty breathing, and insomnia are among the possible side effects of levothyroxine. You should report any potential side effect to your healthcare provider right away, as it may be a symptom of hyperthyroidism and an indication that your levothyroxine dosage is too high. Also, seek immediate medical attention if you notice any signs of an allergic reaction -- another possible levothyroxine side effect.

An Introduction to Levothyroxine Side Effects

As with any medicine, side effects are possible with levothyroxine sodium. However, not everyone who takes the drug will experience side effects. In fact, most people tolerate it quite well.
 
(This article covers many, but not all, of the possible side effects with levothyroxine. Your healthcare provider can discuss a more complete list of levothyroxine side effects with you.)
 

Possible Side Effects of Levothyroxine

Just like any medication, levothyroxine can cause allergic reactions. Seek medical attention immediately if you develop any signs of an allergic reaction, including:
 
  • Wheezing or difficulty breathing
  • An unexplained rash
  • Hives
  • Itching
  • Unexplained swelling (especially of the lips, mouth, or throat).
     
Levothyroxine side effects typically occur when the dosage is too high. Too much levothyroxine can cause symptoms of hyperthyroidism (an excess of thyroid hormones). Because hyperthyroidism can be quite dangerous, any of these symptoms should be reported to your healthcare provider, as they may signal that your levothyroxine dosage needs to be decreased. These side effects may include:
 

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Written by/reviewed by: Kristi Monson, PharmD; Arthur Schoenstadt, MD
Last reviewed by: Kristi Monson, PharmD;
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