Sodium Levothyroxine: What is it? Warnings, Administration, Analysis and Side Effects

It is a medicine used to treat an underactive thyroid gland (hypothyroidism).

The thyroid gland produces thyroid hormone, which helps control energy levels and growth. Levothyroxine is taken to replace the missing thyroid hormone.

Levothyroxine is available only with a prescription. It comes in tablets or as a liquid.

Key facts

Levothyroxine starts working right away, but it can be several weeks before your symptoms start to improve.

The most common side effects of levothyroxine are caused by taking a higher dose than you need. Your doctor may reduce your dose to help reduce side effects.

Before you start taking levothyroxine, your doctor will do a blood test to see what dose you need. Once you start taking the medication, regular blood tests will be done to see how well it is working.

The doses of levothyroxine should be carefully controlled during pregnancy. If you plan to become pregnant or think you may be pregnant while taking levothyroxine, it is important to visit your doctor to make sure you get the right care for you and your baby.

Levothyroxine is also known by the brand name Eltroxin.


Levothyroxine can be taken by adults and children.

However, levothyroxine is not suitable for some people. Do not take levothyroxine and consult your doctor to discuss your treatment if you have:

  • An allergic reaction to levothyroxine or any other medication in the past an overactive thyroid gland (hyperthyroidism).
  • A health problem that affects your adrenal glands (your doctor can tell you if you are not sure).

Check with your doctor before taking levothyroxine if you have:

  • A heart problem that includes angina , heart disease, or heart failure .
  • High blood pressure
  • He had a heart attack.
  • Diabetes: The dose of your diabetes medication may need changes because levothyroxine can raise blood sugar levels.


Take levothyroxine once a day in the morning, ideally at least 30 minutes before having breakfast or a drink containing caffeine such as tea or coffee.

Both breakfast and caffeinated beverages can prevent your body from taking levothyroxine properly, so it does not work as well.

How much will I take?

Levothyroxine comes in tablets of 25 micrograms, 50 micrograms and 100 micrograms. A microgram (sometimes written μg) is a small amount, 1,000 times smaller than a milligram. You may need to take several different tablets to complete your dose. Your doctor will tell you how many tablets to take each day.

The dose of levothyroxine varies from person to person. Although the initial doses are usually the same, the dose of levothyroxine you take or how quickly you increase your dose will depend on your symptoms, hormone levels, age, and if you have other health problems.

Adults usually start with a dose between 50 micrograms and 100 micrograms taken once a day. This can be increased gradually in a few weeks to between 100 micrograms and 200 micrograms taken once a day.

Some people, such as people over 50 or people with heart disease, may start with a lower dose. If you are taking levothyroxine as a liquid, 5 ml is 25 micrograms, 50 micrograms or 100 micrograms.

How will I take it?

Swallow the tablets whole with a drink of water. Levothyroxine is available in liquid form for children and people who find it difficult to swallow tablets.

If you or your child is taking levothyroxine as a liquid, the pharmacist will usually compensate them. It comes with a syringe or a plastic spoon to help you measure the correct dose. If you do not have one, request one from your pharmacist. Do not use a kitchen teaspoon since it will not give the correct amount.

Blood test

Your doctor will perform periodic blood tests to check the levels of thyroid hormones in your body before and after starting levothyroxine. This will allow your doctor to adjust your dose for you.

At the beginning of treatment, it is likely that blood tests are done frequently. Once your hormone levels are stable, you will usually have a blood test after 4 to 6 months, and then once a year.

You may need blood tests more often if:

  • You are pregnant
  • Start or stop a medication that may interfere with levothyroxine.
  • It has some symptom that could mean that your dose is not entirely correct.

What happens if I forget to take it?

If you forget to take a dose, take it as soon as you remember, unless it is almost time for your next dose. In that case, skip the missed dose. Do not take 2 doses together to make up for the missed dose.

If you miss doses frequently, it may be useful to set an alarm to remind you. You can also ask your pharmacist for advice on other ways to help you remember to take your medication.

What happens if I take too much?

Taking an extra dose of levothyroxine by accident is unlikely to harm it.

Talk to your doctor if:

  • Accidentally you take more than 1 extra dose.
  • You get side effects like an accelerated heart or chest pain. This may not happen immediately, it may be several days before they appear.

Side effects

Once you are taking the correct dose of levothyroxine, the side effects will disappear.

Common side effects:

The common side effects of levothyroxine usually occur because the dose you are taking is more than what you need. These side effects usually go away after taking a lower dose of levothyroxine or stopping treatment.

The common side effects are the same as the symptoms of an overactive thyroid. Talk to your doctor or pharmacist if these side effects bother you or do not go away:

  • Feeling sick, vomiting or having diarrhea.
  • Headache.
  • Feeling restless or excitable, or having trouble sleeping.
  • Redness or sweating
  • Muscle cramps.
  • Tremor, usually from the hands.

Serious side effects:

It occurs infrequently, but some people can have serious side effects when taking levothyroxine.

Tell your doctor immediately if you have:

  • Chest pain.
  • Rapid or irregular heartbeat, palpitations.
  • Serious allergic reaction. In rare cases, it is possible to have a severe allergic reaction to levothyroxine.

Pregnancy and lactation

Levothyroxine is generally safe to take during pregnancy and during breastfeeding.

In fact, it is important to continue taking levothyroxine throughout pregnancy. Having too low or too high levels of thyroid hormone during pregnancy can cause problems for you and your baby.

You will need to have regular blood tests during pregnancy to make sure you are taking the correct dose of levothyroxine for you and your baby. Most women need to take a higher dose of levothyroxine than usual while they are pregnant.

It is usually safe to breast-feed while you are taking levothyroxine. Thyroid hormones pass into breast milk at very low levels that are too small to affect the baby.

If you are breast-feeding, it is important that you continue taking levothyroxine. Your body needs good levels of thyroid hormones to produce enough breast milk to feed your baby.

Fact: Honey and nuts are good for the thyroid.