Thyroid Medications in Pregnancy: Levothyroxine, Neomercazole and Tapazol

Thyroid medications in pregnancy should not be stopped on your own. Levothyroxine usually continues during pregnancy with regular monitoring, and its dose often changes on your doctor's decision [1]. Neomercazole and Tapazole, used to treat an overactive thyroid, require a plan set by an endocrinologist, because the first trimester has special considerations that may include switching to another medication. Tell your doctor as soon as you plan a pregnancy or discover one.

Are thyroid medications safe during pregnancy?

The thyroid is a small gland at the front of the neck that produces hormones controlling how the body uses energy, and it affects the heart, digestion, weight, mood and more [3]. Treating the thyroid during pregnancy is therefore not a luxury, but part of protecting both the mother and the fetus.

Untreated hypothyroidism may increase the risk of serious complications in pregnancy, including high blood pressure (pre-eclampsia), birth defects in the fetus, preterm birth, and miscarriage [1]. According to the same source, treatment usually helps prevent these complications.

For this reason, the right question is not "Should I take the medication or not?" but rather "Which medication is suitable, at what dose, and how will I be monitored?" You can find more detail in our article on Thyroid Disorders in Pregnancy: Diagnosis, Treatment and Maternal and Fetal Impact, and in the answer to the question Can thyroid medications affect the fetus?

Levothyroxine in pregnancy: Should I continue it, and does the dose change?

Levothyroxine (levothyroxine sodium) is the standard medication for hypothyroidism. It replaces the hormone the body cannot produce, and it usually needs to be taken for life to prevent the return of symptoms [1]. During pregnancy it should not be stopped, as the body needs this hormone more than at any other time.

Medical references advise women with hypothyroidism who are pregnant or planning a pregnancy to inform their doctor, so that additional tests can be done. The levothyroxine dose is likely to change during pregnancy [1]. In practice, the adjustment is often an increase, but its amount and timing are determined by the doctor based on test results, not by a fixed rule.

Practical tips for taking levothyroxine

• Follow the usual dose set by your doctor or pharmacist, without increasing or decreasing it on your own.
• An incorrect dose, whether too high or too low, may cause nausea, diarrhea, headache or sleep disturbance [1]. If these symptoms appear, tell your doctor or pharmacist.
• Some supplements, including those containing iron or calcium, may affect the absorption of levothyroxine. Ask your pharmacist about the appropriate interval between them and the medication.
• If you vomit after a dose or forget a dose, ask your doctor or pharmacist what to do, and do not double the next dose on your own.

To learn more about the condition itself, read Hypothyroidism: Causes, Symptoms and Treatment.

How are TSH and thyroid hormones monitored during pregnancy?

Monitoring relies on blood tests, most importantly thyroid-stimulating hormone (TSH) and thyroxine (T4). These are thyroid tests that doctors use for diagnosis and follow-up [1][3]. You can learn what the results mean on the page Thyroid Function Tests (TSH, T4).

The British source confirms that people with hypothyroidism have regular blood tests to check that the dose is appropriate [1]. The number and timing of tests during pregnancy are determined by your doctor. The following is a general outline of the stages:

Why does testing matter even before symptoms appear? Because symptoms of hypothyroidism may be mild and develop slowly [1], and during pregnancy they may be attributed to normal tiredness. See also The Importance of Thyroid Screening Before and During Pregnancy.

Neomercazole and Tapazole in pregnancy: When do they require a special decision?

Overactive thyroid is often treated with medications from the thionamide class, the best known being carbimazole and propylthiouracil (PTU). The patient is usually referred to an endocrinologist who sets the plan [2]. Neomercazole contains carbimazole, and Tapazole contains methimazole, and both belong to the same therapeutic family.

References state that taking carbimazole during pregnancy may harm the fetus, and that a woman should use effective contraception throughout treatment and inform her doctor immediately if she becomes pregnant while taking it [2]. According to the ClinicsJo drug guide, use of these medications early in pregnancy has been associated with defects of the skin and skull. For this reason, propylthiouracil is often substituted in the first trimester, and the doctor then decides whether the first medication should be resumed afterward.

What does this mean in practice?

• Do not stop suddenly: Uncontrolled overactive thyroid is not without risk, and changing or stopping the medication is a decision made by the specialist after examining you.
• Do not wait for your next appointment: If you discover you are pregnant while taking one of these medications, call your doctor the same day.
• Do not judge your improvement by how you feel: It is advised not to stop the medication when you feel better, because stability is built over months of treatment and is confirmed by tests.
• Follow up carefully: Treatment usually lasts 12 to 18 months, and some patients may need years or lifelong treatment [2]. A beta-blocker may be given to temporarily relieve symptoms [2].

The usual dose set by the doctor varies widely from patient to patient, and it is gradually reduced once hormone levels are controlled [2]. It is natural for a doctor during pregnancy to aim for the lowest dose that keeps hormones under control. For more about the condition: Hyperthyroidism: Symptoms, Causes and Treatment.

Thyroid medications in pregnancy when planning: What should you do before you conceive?

Advance planning eases a great deal of anxiety. If you are taking a thyroid medication and thinking about pregnancy, talk with your doctor before stopping contraception, so they can determine the most suitable medication and the right timing.

1. Tell your doctor your plan: so the dose and tests can be reviewed before conception [1].
2. Control your hormones first: Ideally, the condition should be under control before pregnancy.
3. Discuss the options: For overactive thyroid there are three main treatments: medication, radioactive iodine and surgery [2]. The choice depends on the severity of the condition, your symptoms and your plans for having children [3].
4. Pay attention to the timing of radioactive iodine: It is not suitable for pregnant or breastfeeding women. Women are advised to avoid pregnancy for at least six months after it, and men are advised not to father children for at least four months [2].
5. If surgery is performed: Removal of the entire gland requires lifelong levothyroxine [2], and adjusting its dose becomes part of the pregnancy plan.

For a broader picture of medication safety in pregnancy in general, you can read Medications and Pregnancy: A Comprehensive Guide to Maternal and Fetal Safety.

Quick comparison of thyroid medications in pregnancy

The following table is for simplification only and is not a substitute for your doctor's plan:

When should you see a doctor, and when should you go to the emergency room?

See your doctor as soon as possible if:

• You become pregnant or suspect pregnancy while taking any thyroid medication.
• Symptoms of hypothyroidism appear, such as severe fatigue, feeling cold, constipation, hair loss and hoarseness [1].
• Symptoms of a dose that is too high or too low appear, such as nausea, diarrhea, headache or sleep disturbance [1].
• A skin rash, itching or joint pain appears after starting an antithyroid medication, as these may be among its common mild side effects [2].

Request urgent testing or go to the emergency room if:

• You develop fever, sore throat, persistent cough or mouth ulcers while taking neomercazole, Tapazole or PTU. These may be a sign of a sudden drop in white blood cells (agranulocytosis), and a blood count is needed the same day [2]. Tell the emergency staff that you are taking this medication.
• Your eyes or skin turn yellow, which requires a liver test.
• You have vaginal bleeding, severe abdominal pain, or severe headache with visual disturbance or sudden swelling, or your baby's movements decrease.
• You experience severe palpitations, shortness of breath, confusion, or rapid general deterioration.

In emergencies, call 911 or go to the nearest emergency department.

How do you find the right endocrinologist in Jordan?

Ideally, your case should be followed by an endocrinologist in coordination with an obstetrician-gynecologist. You can browse Endocrinologists and Diabetes Specialists in Jordan, or search by governorate: Amman, Irbid or Zarqa. You can also find an explanation of the Thyroid Medication Prescribing Service.

What to check in the doctor's profile

• The specialty (endocrinology) and the stated experience in thyroid disease.
• The clinic location, working days, and the contact or booking methods available in the profile.
• Whether the profile mentions following pregnant women or collaborating with obstetricians.

Useful questions to ask at the appointment

1. Should I continue my current dose, and when should TSH be rechecked?
2. If I am taking a medication for overactive thyroid, does it need to be changed in the first trimester?
3. What symptoms should prompt me to call you immediately?
4. What is the appropriate interval between levothyroxine and prenatal vitamins or supplements?
5. Who will monitor my dose after delivery?

You may also start at maternal and child health centers and the primary health care centers run by the Ministry of Health across the governorates, to coordinate general pregnancy follow-up, and then be referred to the specialist when needed.

Common mistakes to avoid

• Stopping the medication out of fear for the fetus: The greater danger may come from leaving the disease untreated, as the complications mentioned earlier are linked to untreated hypothyroidism [1].
• Adjusting the dose based on a friend's advice: The dose depends on your own test results.
• Using herbs or supplements "to regulate the thyroid": Consult your doctor and pharmacist first. For more on safe use, see Drug Safety: A Consumer Guide.
• Neglecting testing after delivery: The body's need for medication may change after pregnancy ends.

As a reminder, this information is educational and does not replace an evaluation by your doctor. In Jordan, medications and their general prices are regulated under the supervision of the Jordan Food and Drug Administration (JFDA). Always ask your pharmacist about the registered medication available to you and its approved alternatives before any change.

Frequently asked questions

Should I continue levothyroxine if I become pregnant?

Yes, in most cases. Levothyroxine replaces a hormone the body needs, and you should inform your doctor as soon as you plan a pregnancy or discover one. You will have blood tests, and the dose is likely to change during pregnancy. Do not adjust the dose yourself; follow what your doctor or pharmacist determines based on your test results.

Can I stop neomercazole or Tapazole when I discover I am pregnant?

Do not stop it on your own. Call your doctor the same day so they can decide on the plan. The medication may be replaced with another one in the first trimester, and the choice will be reviewed afterward. Uncontrolled overactive thyroid may harm both the mother and the pregnancy, so the matter requires specialist assessment rather than an individual decision.

Why is carbimazole replaced with propylthiouracil early in pregnancy?

Because according to the drug guide, use of carbimazole and methimazole early in pregnancy has been associated with defects of the skin and skull, so doctors often prefer propylthiouracil in the first trimester. The decision rests with the endocrinologist, the new medication is monitored with tests, and the choice is reviewed later.

What symptoms require an immediate blood test while taking overactive thyroid medication?

Sudden fever, sore throat, persistent cough or mouth ulcers may indicate a drop in white blood cells, a rare but serious side effect. Request a blood count the same day and tell the emergency doctor which medication you are taking. Yellowing of the eyes or skin requires a liver test.

Can I take radioactive iodine if I am planning a pregnancy?

Radioactive iodine is not suitable for pregnant or breastfeeding women. Women are advised to avoid pregnancy for at least six months after it, and men are advised not to father children for at least four months. Discuss your options and their timing with your endocrinologist before making any decision, as there may be alternatives that suit your plans for having children.

How often is TSH tested during pregnancy?

There is no fixed number that suits everyone. Your doctor sets the testing schedule based on the type of condition, the medication and your previous results. In general, regular blood tests are done to confirm that the dose is appropriate, and they are repeated after any adjustment. Keep your previous results and bring them with you to every visit.

Sources and references

1. Underactive thyroid (hypothyroidism) — NHS (UK National Health Service). Accessed: 2026-10-26.
2. Overactive thyroid (hyperthyroidism) - Treatment — NHS (UK National Health Service). Accessed: 2026-10-26.
3. Thyroid Diseases | Hypothyroidism | Hyperthyroidism — MedlinePlus — U.S. National Library of Medicine. Accessed: 2026-10-26.