Note: This document contains side effect information about methimazole. Some of the dosage forms listed on this page may not apply to the brand name Tapazole.
Applies to methimazole: oral tablet
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
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
Applies to methimazole: compounding powder, oral tablet
Some of the more frequently reported adverse reactions have included skin rash, urticaria, nausea, loss of taste, and abnormal loss of hair.
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.
Frequency not reported: Lymphadenopathy, agranulocytosis, granulocytopenia, thrombocytopenia, aplastic anemia, hypoprothrombinemia
Frequency not reported: Lupus-like syndrome
Frequency not reported: Jaundice, hepatitis
Frequency not reported: Edema, periarteritis
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.
Frequency not reported: Skin rash, urticaria, abnormal loss of hair, pruritus, skin pigmentation
Frequency not reported: Arthralgia, myalgia
Frequency not reported: Paresthesia, loss of taste, headache, drowsiness, neuritis
Frequency not reported: Nausea, vomiting, epigastric distress, sialadenopathy
Very rare (less than 0.01%): Nephritis
Frequency not reported: Insulin autoimmune syndrome
Frequency not reported: Vertigo, drug fever
Medically reviewed by BestRx Medical Team Last updated on 1/1/2020.
Source: Drugs.com Tapazole