You are caring for a client with hypothyroidism that is taking levothyroxine (Synthroid). The client reports diarrhea, weight loss, palpitations, and heat intolerance. You suspect which of the following adverse effects of this drug?

A. Hypothyroidism: This is incorrect. The client is taking levothyroxine (Synthroid) to treat hypothyroidism, and the symptoms described (diarrhea, weight loss, palpitations, heat intolerance) are more likely associated with excess thyroid hormone, not a lack of it. B. Thyrotoxicosis: This is correct. The symptoms the client is experiencing—diarrhea, weight loss, palpitations, and heat intolerance—are classic signs of thyrotoxicosis, which occurs when there is an excess of thyroid hormone, possibly due to overtreatment with levothyroxine. These symptoms indicate that the thyroid hormone dose might need adjustment. C. Addison's Disease: This is incorrect. Addison's disease is characterized by insufficient production of adrenal hormones and would typically manifest with symptoms such as fatigue, hypotension, and hyperpigmentation, not diarrhea or heat intolerance. D. Cushing's Disease: This is incorrect. Cushing's disease is caused by excess cortisol and would typically result in symptoms such as weight gain, high blood pressure, and a round "moon" face, rather than the symptoms described in the question.