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Levothroid Warnings and Precautions

Before taking Levothroid, warnings and precautions for the drug should be reviewed to avoid possible complications. For example, it is important to know that the medication may increase your risk of osteoporosis and can make heart problems worse. It is important to tell your healthcare provider if you have any other medical conditions (such as diabetes, adrenal insufficiency, or any allergies) and if you are taking any other medications.

Levothroid: What Should I Tell My Healthcare Provider?

You should talk with your healthcare provider prior to taking Levothroid® (levothyroxine sodium) if you have:
Also, let your healthcare provider know if you are:
  • Pregnant or thinking of becoming pregnant
  • Breastfeeding.
Make sure to tell your healthcare provider about any other medicines you are taking, including prescription and non-prescription medicines, vitamins, and herbal supplements.

Specific Levothroid Warnings and Precautions

Some of the warnings and precautions to be aware of prior to taking Levothroid include the following:
  • People who do not have thyroid problems should never use Levothroid to lose weight. A Levothroid dosage high enough to cause weight loss in these people is often high enough to cause serious or even life-threatening problems.
  • Sometimes, thyroid problems occur in conjunction with other health problems (such as anemia or diabetes). It is a good idea for your healthcare provider to give you a thorough physical exam when you are diagnosed with a thyroid problem.
  • Levothroid is a "narrow therapeutic index" medication. This means that for any given person, the range of Levothroid doses that are both safe and effective is small. Even tiny changes in doses can cause significant problems (either making Levothroid ineffective or causing serious side effects). Your healthcare provider should carefully and slowly adjust your dose, and should monitor your progress often using blood tests. Even if you have been stable on Levothroid for years, your healthcare provider should still do these blood tests regularly.
  • Levothroid can make heart problems worse. If you have heart problems, your healthcare provider should start you at a low Levothroid dosage and slowly increase it. If you notice that Levothroid makes your heart symptoms worse, let your healthcare provider know right away.
  • Levothroid should not be used to treat goiters or thyroid nodules in people who have a low level of thyroid-stimulating hormone (TSH), as it could cause dangerous side effects. A low TSH level signals that thyroid hormone levels are already high, and adding Levothroid could cause them to increase to a dangerous level. Even if the TSH level is normal, frequent monitoring is required to make sure problems do not develop.
  • Levothroid may increase the risk of osteoporosis, particularly if your Levothroid dose is too high. This is one of the reasons why it is a good idea for your healthcare provider to prescribe a dose of Levothroid that is just enough to return your thyroid hormone levels to normal. 
It often takes Levothroid several weeks to start working. Try not to get frustrated if you are not feeling better more quickly.
  • If you have diabetes, it is a good idea to check your blood sugar more often when starting or stopping Levothroid (or when changing your dose), as the medication can affect your blood sugar levels.
  • Levothroid can potentially interact with many other medications (see Levothroid Drug Interactions).
  • Levothroid is considered a pregnancy Category A medication. This means that it is safe for use during pregnancy (see Levothroid and Pregnancy).
  • Levothroid does pass through breast milk in humans, although it is not likely to cause problems. If you are breastfeeding or plan to start breastfeeding, discuss this with your healthcare provider prior to taking the drug (see Levothroid and Breastfeeding).
Last reviewed by: Kristi Monson, PharmD
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