Thyroid disorders can be a cause of hyponatremia, or low blood sodium, which is why you may associate thyroid medication with low blood sodium. However, thyroid medications do not typically cause hyponatremia; in fact, they may help to prevent it.
Low Blood Sodium
Low blood sodium, also known as hyponatremia, can be a dangerous condition. According to the Linus Pauling Institute, sodium helps to control the systems that send nerve impulses, contract muscles and maintain heart function. Without enough sodium, your cells can begin to swell and retain fluid, leading to complications like headaches, nausea and vomiting, muscle cramps, disorientation, fainting and fatigue. In sudden or severe cases, it can even cause seizures, brain swelling, brain damage, coma and death.
Hypothyroidism
One of the common causes of low blood sodium is hypothyroidism, or a hormonal imbalance due to a thyroid malfunction. According to the National Institutes of Health, hypothyroidism is a condition in which your thyroid gland does not produce enough hormones, which normally help to control your metabolism. Hyponatremia can be a symptom of hypothyroidism, while other symptoms can include fatigue, temperature sensitivity, depression, joint and muscle pain. Other side effects can also include anemia and increased cholesterol.
Other Causes
Low blood sodium can be caused by other factors, not just hypothyroidism. Some medications -- particularly antidepressants and pain medications -- may lead to hyponatremia. Excessive sweating and dehydration can also lead to sodium depletion. In unusual cases, thyroid medication can cause excessive sweating; however, this is a rare side effect. Other causes of hyponatremia can include kidney problems, liver cirrhosis, congestive heart failure, and severe vomiting or diarrhea.
Side Effects of Thyroid Medications
Normally, thyroid medications help to correct hypothyroidism, which can actually cause low blood sodium. In rare cases, these medications may cause excessive sweating, which could lead to low blood sodium. Consult a physician if your thyroid medication is causing unusual and extreme sweating. However, more typical side effects include weight loss, headache, nausea and vomiting, stomach cramps, mood swings, insomnia, menstrual cycle changes and anxiety. Rare and serious side effects can also include difficulty breathing, heart arrhythmias, chest pain and seizures.
