Hyperthyroidism is a condition that occurs when your thyroid gland produces too much thyroid hormones. It’s often referred to as overactive thyroid or Graves’ disease.

Several types of cancer treatment may cause thyroid problems, like thyroid inflammation (thyroiditis), underactive thyroid (hypothyroidism), and hyperthyroidism.

However, very limited research has established a link between chemotherapy drugs specifically and overactive thyroid.

Some research suggests that a chemotherapy drug called cyclophosphamide may cause hyperthyroidism.

According to the Canadian Cancer Society, the following cancer treatments are associated with thyroid disorders:

  • alkylating chemotherapy drugs, such as cyclophosphamide (Procytox) or busulfan
  • tyrosine kinase inhibitors, such as imatinib (Gleevec) and dasatinib (Sprycel)
  • alemtuzumab (Lemtrada), a type of monoclonal antibody

A newer type of immunotherapy, called immune checkpoint inhibitors (ICIs), may also lead to hyperthyroidism. Immunotherapy targets the immune system to help it fight off infections and kill cancer cells.

A 2020 study involving 168 people receiving treatment with ICIs found that 34 people developed hypothyroidism and 20 people developed hyperthyroidism.

Limited research has examined the onset time of hyperthyroidism after starting chemotherapy specifically.

In the same 2020 study, researchers found that, on average, thyroid problems occurred 2.8 months after starting treatment with ICIs. The researchers did not specify how long it took to develop hyperthyroidism.

Abnormal thyroid activity related to immunotherapy usually stems from thyroid inflammation. This typically causes a pattern that begins with hyperactive and then shifts to hypoactive in 6 to 9 months.

When receiving ICI treatment, however, the shift from hyperactive to hypoactive thyroid may only take 3 months.

More research is needed to better understand the onset time of hyperthyroidism after starting chemotherapy.

The symptoms of hyperthyroidism differ for each individual, and some of them may be similar to the possible side effects of chemotherapy.

Symptoms of hyperthyroidism may include:

If you experience any of these symptoms after starting chemotherapy, speak with your doctor. They could perform thyroid function tests and other blood tests to help determine the underlying cause of your symptoms.

Should you get your thyroid checked if you’re receiving cancer treatment?

According to a 2023 review, healthcare organizations recommend checking thyroid function every 1 to 2 months during treatment with ICIs, and every 3 to 6 months after treatment.

Several medications may help treat hyperthyroidism caused by cancer treatment, such as:

The drugs propranolol and atenolol can also help manage hyperthyroidism symptoms and your response to ICIs.

Speak with your doctor if you experience symptoms of hyperthyroidism and are receiving chemotherapy or other types of cancer treatment. They could help develop the best treatment plan for you.