What are the possible side effects of Synthroid (levothyroxine)?

Most of the side effects of Synthroid (levothyroxine) are caused by taking too much of the medication. An overdose of Synthroid may cause hyperthyroidism, or overactive thyroid. Symptoms of an overactive thyroid include: increased sweating, fever, flushing, inability to tolerate heat, increased appetite, weight loss, anxiety, nervousness, irritability, hyperactivity, difficulty sleeping, weakness, joint pain, leg cramps, broken bones, osteoporosis, emotional changes, hair loss, headaches, shakiness, seizures, vomiting, diarrhea, stomach cramps, menstrual changes, fertility difficulties, high blood pressure, difficulty breathing and pain while breathing. Allergic reactions to Synthroid include rash, itching and swelling. Heart problems may also occur. Such heart problems include: a fast or irregular heartbeat, palpitations, heart failure, chest pain or heart attack.

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Are palpitations a side effect of thyroid supplement?
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