What is a common side effect of excess levothyroxine in patients?

Excess levothyroxine can lead to a range of symptoms typically associated with hyperthyroidism, reflecting the drug's role in increasing metabolic activity and stimulating various physiological systems. Palpitations occur as a common side effect due to the increased heart rate and enhanced heart contractility induced by excessive thyroid hormone levels. When levothyroxine is taken beyond the therapeutic range, it can cause stimulatory effects on the cardiovascular system, leading to an increased heart rate and sensations of rapid heartbeats—described as palpitations. These symptoms are particularly concerning as they can lead to more severe cardiovascular issues if not addressed.

In contrast, weight gain, hypoglycemia, and fluid retention are not directly associated with excess levothyroxine use. Weight gain is typically linked to hypothyroidism rather than hyperthyroidism. Hypoglycemia can occur in certain contexts, but it's not a standard side effect of thyroid hormone excess. Fluid retention might also occur, but it is less characteristic when compared to the enhanced metabolic effects leading to palpitations. Thus, the most relevant and commonly observed consequence of taking too much levothyroxine is the presence of palpitations.