You may be able to take other medications with levothyroxine, but some of them will have to be taken at a different time from when you take your levothyroxine.

• Levothyroxine is known to interact with many other medications (called a drug-drug interaction), but there are different kinds of drug-drug interactions.
• Some interactions require that drugs not be taken at the same time, while other interactions require more frequent laboratory testing or monitoring of your disease symptoms.

For drug interactions that result in binding of the levothyroxine and therefore decreased absorption of the drug from the intestine, it is very important to avoid taking the interacting medicine at the same time as levothyroxine. In fact, it is recommended to separate the administration of these medicines from levothyroxine by 4 hours.

The medicines and supplements that should not be taken within 4 hours of taking levothyroxine include:

• Calcium supplements (including those found in multivitamins)
• Iron supplements (including those found in multivitamins)
• Antacids
• Sucralfate
• Phosphate binders (calcium carbonate, ferrous sulfate, sevelamer, lanthanum)
• Bile acid sequestrants (colesevelam, cholestyramine, colestipol)
• Ion exchange resins (kayexalate)

Sometimes drug interactions cannot be avoided because both medicines may be very important to your treatment. In the case of levothyroxine, you may need more frequent testing of thyroid stimulating hormone and T4 levels when other medications are added or removed from your treatment regimen. After another drug has been added to or removed from your regimen, you should report worsening of any disease symptoms or medication side effects to your doctor.

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How to take levothyroxine

Levothyroxine should be taken once a day on an empty stomach. Usually it should be taken at least 30 to 60 minutes before eating breakfast, or at bedtime (3 or more hours after the evening meal). Taking it on an empty stomach results in the best absorption of the drug from the intestine.

If you are unsure whether one of your medicines interacts with levothyroxine, talk to your doctor or pharmacist. Make sure to always give all of your healthcare providers a full list of your medications (prescription and nonprescription) and any supplements you take. This will help you and your doctors to evaluate all possible interactions and come up with a plan to avoid or minimize them.

Levothyroxine and hypothyroidism

Levothyroxine is a man-made form of the human thyroid hormone called T4. It is given to people who do not produce enough of their own thyroid hormone (hypothyroidism).

Some of the common symptoms of hypothyroidism include:

• Constant fatigue
• Weight gain and fluid retention
• Constipation
• Dry itching skin
• Dry, brittle hair and nails
• Difficulty learning or remembering
• Sensitivity to cold temperatures

The effectiveness of levothyroxine therapy is measured by monitoring your symptoms and by checking the amount of two main thyroid-related hormones—thyroid stimulating hormone and T4—in the blood. Levothyroxine is usually started at a low dose and slowly increased over time. The full effects of levothyroxine may take weeks to months to realize. With hypothyroidism, you will need to take thyroid replacement such as levothyroxine for the rest of your life.