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Risk of pancreatitis with methimazole

Clinical Thyroidology for the Public

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Methimazole is an effective medication that is used to treat hyperthyroidism. Methimazole is taken up by the thyroid and interferes with the production of thyroid hormone. While usually well tolerated, there are side effects to methimazole that can require stopping therapy. Well-known side effects that require stopping therapy are agranulocytosis (low white blood cell levels that can lead to infection) and inflammation of the liver. These side effects are rare, occurring in 1 in 500-1000 patients and is often related to the dose of methimazole.

There have been some reports of acute pancreatitis (a condition that results from the inflammation of the pancreas) from methimazole. This study was done to understand the risk of this condition for patients were taking methimazole and compared with the general population.

Pecere A et al 2020 Methimazole treatment and risk of acute pancreatitis: A population-based cohort study. J Clin Endocrinol Metab 105:dgaa544. PMID: 32813014.

About 4.4 million residence of the Piedmont region of Italy were studied. The study looked at the hospital discharge records to compare the frequency of acute pancreatitis spanning the period 2013–2018 among new methimazole users with those who had never used methimazole. Hospital admissions during the first 18 months of methimazole use were subdivided into 3-month periods for analysis.

Methimazole was started in 23,087 patients during the 5-year study period. There were 61 patients (0.3%) hospitalized with acute pancreatitis during the first 18 months of methimazole treatment, with only 13 of the 61 admissions occurring during the first 3 months of therapy; 4 individuals died while hospitalized. The risk for acute pancreatitis was significantly increased among methimazole users as compared with those who had never used methimazole during the first 9 months of methimazole therapy. Thereafter, these was no difference between the risk acute pancreatitis between the 2 groups. Additionally, the absolute risk increased with age—for example, in the 18-to-39-year-old age group, the risk of acute pancreatitis was 0.02% in men and 0.05% in women, while in the 40-to-59-year-old age group, the calculated risks increased to 0.09% and 0.08%, respectively. There was no difference between male and female patients.

This study shows that there is likely a very low but significant risk of developing acute pancreatitis during the initial few months of methimazole treatment. Even though the overall risk was low it is important to educate patients and doctors regarding this possible complication from methimazole therapy. Further studies are needed to define this risk and understand the underlying causes.

— Vibhavasu Sharma, MD, FACE


Hyperthyroidism: a condition where the thyroid gland is overactive and produces too much thyroid hormone. Hyperthyroidism may be treated with antithyroid meds (Methimazole, Propylthiouracil), radioactive iodine or surgery.

Methimazole: an antithyroid medication that blocks the thyroid from making thyroid hormone. Methimazole is used to treat hyperthyroidism, especially when it is caused by Graves’ disease.

Acute pancreatitis: acute inflammation of the pancreas, usually caused by gallstones or alcohol use. This can lead to hospitalization and death depending upon the cause and the severity of the inflammation.


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