Recently, Hillary Clinton left a 9/11 memorial service early because she’s been battling a bout of walking pneumonia while stumping. But the presidential nominee is also living with another health issue: hypothyroidism, reports the Washington Examiner.

Hypothyroidism occurs when the thyroid gland, an organ located in the throat, is underactive and doesn’t produce enough thyroid hormone. The resulting symptoms include fatigue, weakness and weight gain. The condition affects more than 10 million Americans and, for most people, is highly treatable with via hormone therapy.

Clinton, 68, is currently taking a medication called Armour Thyroid that effectively treats her underactive thyroid with a combination therapy of the thyroid hormones T3 and T4. Clinton’s doctor noted that the candidate is in “excellent” physical condition while living with the disorder.

Typically, people diagnosed with hypothyroidism are prescribed a single hormone replacement called levothyroxine. This medication is effective in about 90 percent of the cases it’s used to treat. But it appears that Clinton may fall into the small subset of people who do not respond to the traditional treatment for hypothyroidism.

“She is perfectly capable and in good health, taking her medication,” said Hossein Gharib, MD, a doctor at the Mayo Clinic and former president of the American Association of Clinical Endocrinologists.  “This is in no way an impediment or deterrent [to Clinton running for president]. She is a normal human being at this point.”

As she continues her run for the Oval Office, Clinton promised to publish more in-depth information about her medical records and hypothyroidism during the next few weeks.

Click here to learn more about the effects of hypothyroidism and the treatment for this illness.