What is a potential side effect of levothyroxine?

Levothyroxine is a synthetic form of the thyroid hormone thyroxine (T4) and is used primarily to treat hypothyroidism. One of the well-known side effects of levothyroxine is an increased heart rate, or tachycardia. This occurs because levothyroxine can lead to an elevation in metabolic rate and increase the heart's workload as the body begins to metabolize at a higher rate. Patients taking this medication may experience palpitations or a fast heart rate, especially if the dosage is too high or when treatment is initiated too rapidly.

In contrast, weight gain is typically not associated with levothyroxine treatment; rather, it is intended to alleviate symptoms of hypothyroidism, which often include weight gain. Hypotension is not a common side effect of this medication; instead, elevated blood pressure can sometimes occur due to improved metabolic function. Sleepiness, while it may occur in some individuals, is more often associated with hypothyroidism itself prior to treatment rather than a side effect of levothyroxine.

Overall, understanding the metabolic effects of levothyroxine on cardiovascular function highlights why a fast heart rate is a significant and recognized potential side effect.