Tapazole Side Effects

Generic name: methimazole

Medically reviewed by Drugs.com. Last updated on Dec 16, 2023.

Note: This document provides detailed information about Tapazole.

Applies to methimazole: oral tablet Side Effects associated with methimazole. Some dosage forms listed on this page may not apply specifically to the brand name Tapazole.

Applies to methimazole: oral tablet.

Precautions

It is very important that your doctor check your or your child's progress at regular visits to make sure that the medicine is working properly. Blood and urine tests may be needed to check for unwanted effects.

Using this medicine during the first three months of your pregnancy can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using the medicine, tell your doctor right away.

In very rare situations, methimazole (the active ingredient contained in Tapazole) can temporarily lower the number of white blood cells in your blood, which increases the chance of getting an infection. It can also lower the number of platelets, which are necessary for proper blood clotting. If this occurs, there are certain precautions you can take, especially when your blood count is low, to reduce the risk of infection or bleeding:

• If you can, avoid people with infections. Check with your doctor immediately if you think you are getting an infection or if you get a fever or chills, cough or hoarseness, lower back or side pain, or painful or difficult urination.
• Check with your doctor immediately if you notice any unusual bleeding or bruising, black, tarry stools, blood in the urine or stools, or pinpoint red spots on your skin.
• Be careful when using a regular toothbrush, dental floss, or toothpick. Your medical doctor, dentist, or nurse may recommend other ways to clean your teeth and gums. Check with your medical doctor before having any dental work done.
• Do not touch your eyes or the inside of your nose unless you have just washed your hands and have not touched anything else in the meantime.
• Be careful not to cut yourself when you are using sharp objects such as a safety razor or fingernail or toenail cutters.
• Avoid contact sports or other situations where bruising or injury could occur.

Check with your doctor right away if you have pain or tenderness in the upper stomach, pale stools, dark urine, loss of appetite, nausea, vomiting, or yellow eyes or skin. These could be symptoms of a serious liver problem.

This medicine may cause hypothyroidism (low levels of thyroid hormone in the blood). Check with your doctor right away if you have constipation, a depressed mood, dry skin and hair, feeling cold, hair loss hoarseness or husky voice, muscle cramps and stiffness, slowed heartbeat, weight gain, or unusual tiredness or weakness.

Make sure any doctor or dentist who treats you knows that you are using this medicine.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

Serious side effects of Tapazole

Along with its needed effects, methimazole may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking methimazole:

Other side effects of Tapazole

Some side effects of methimazole may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

For healthcare professionals

Applies to methimazole: compounding powder, oral tablet.

General adverse events

Some of the more frequently reported adverse reactions have included skin rash, urticaria, nausea, loss of taste, and abnormal loss of hair.

Hematologic

• Frequency not reported: Lymphadenopathy, agranulocytosis, granulocytopenia, thrombocytopenia, aplastic anemia, hypoprothrombinemia^[Ref]

The onset of aplastic anemia (pancytopenia) or agranulocytosis may occur in hours to days. Most cases of agranulocytosis occur within the first 90 days of treatment, but this complication can occur even a year or more after starting therapy.

Studies have suggested that the risk of agranulocytosis is greater in older patients and that they have a higher rate of death.^[Ref]

Immunologic

• Frequency not reported: Lupus-like syndrome^[Ref]

Hepatic

• Frequency not reported: Jaundice, hepatitis^[Ref]

Cardiovascular

• Frequency not reported: Edema, periarteritis

Dermatologic

• Frequency not reported: Skin rash, urticaria, abnormal loss of hair, pruritus, skin pigmentation^[Ref]

A 5-year-old female experienced aplasia cutis congenita coincident with in utero exposure to methimazole. She presented with hairless scars on her scalp. At birth the lesions were friable and bled easily, however, over time they became scar-like and thicker. At the time of conception, her mother was receiving therapy for Graves' disease with methimazole 20 mg daily. Aplasia cutis congenita has been reported as a possible teratogenic effect of methimazole therapy in multiple case reports. However, the causal relationship between the therapy and the skin defect is controversial, and anomalies related to methimazole have low birth prevalence.^[Ref]

Musculoskeletal

• Frequency not reported: Arthralgia, myalgia^[Ref]

Nervous system

• Frequency not reported: Paresthesia, loss of taste, headache, drowsiness, neuritis^[Ref]

Gastrointestinal

• Frequency not reported: Nausea, vomiting, epigastric distress, sialadenopathy
• Postmarketing reports: Acute pancreatitis^[Ref]

Case reports for recurrent acute pancreatitis with a decreased time to onset after re-exposure to carbimazole/thiamazole (methimazole) have been received. The mechanism is not completely understood, but the presentation suggests an immunological mechanism.^[Ref]

Renal

• Very rare (less than 0.01%): Nephritis^[Ref]

Metabolic

• Frequency not reported: Insulin autoimmune syndrome

Other

• Frequency not reported: Vertigo, drug fever^[Ref]

See also:

Frequently asked questions

• Does methimazole cause hair loss?

Further information

Tapazole side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer