Depending on the type of thyroid medication taken, such as levothyroxine sodium, which is used to address hypothyroidism (underactive thyroid), too much thyroid medication may cause transient symptoms similar to those of hyperthyroidism (overactive thyroid). In this case, the patient may experience excessive sweating, rapid heartbeat, anxiety, diarrhea, weight loss, feeling jittery, shaking hands, and trouble sleeping.
Conversely, if the medication is addressing hyperthyroidism and the dose is too high, the patient may experience the opposite feelings of lethargy, lower heartbeat, feeling cold, depression, and mood swings.