Tapazole Side Effects

Generic name: methimazole

Medically reviewed by Drugs.com. Last updated on Jan 5, 2023.

Note: This document contains side effect information about methimazole. Some dosage forms listed on this page may not apply to the brand name Tapazole.

Applies to methimazole: oral tablet.

Serious side effects of Tapazole

Along with its needed effects, methimazole (the active ingredient contained in Tapazole) 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:

Incidence not known

Black, tarry stools
bleeding gums
bleeding under the skin
bloody or cloudy urine
burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
chest pain
chills
cough
dark urine
difficulty in breathing
dizziness or lightheadedness
drowsiness
feeling of constant movement of self or surroundings
fever
general feeling of discomfort, illness, or weakness
headache
hoarseness
itching, skin rash
light-colored stools
loss of appetite and weight
loss of consciousness
lower back or side pain
nausea
painful or difficult urination
pinpoint red spots on the skin
redness, soreness, or itching skin
sensation of spinning
sore throat
soreness of the muscles
sores, ulcers, or white spots on the lips or in the mouth
sores, welts, or blisters
stomach pain
swelling of the face, feet, or lower legs
swollen or painful glands
swollen salivary glands
swollen, painful, or tender lymph glands in the neck, armpit, or groin
tightness in the chest
unusual bleeding or bruising
unusual tiredness or weakness
unusual weight gain
upper right abdominal pain
yellow eyes or skin

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:

Incidence not known

Abnormal loss of hair
changes in skin coloring
difficulty in moving
heartburn
joint pain or swelling
loss of taste
muscle pain, cramps, or stiffness
pain or discomfort in the chest, upper stomach, or throat

For Healthcare Professionals

Applies to methimazole: compounding powder, oral tablet.

General

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

A 5-year-old female experienced aplasia cutis congenita coincident with in utero exposure to methimazole (the active ingredient contained in Tapazole) 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]

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