Side effects associated with thyroid medications vary depending on the type of drug the patient is taking.

About 5 percent of patients may have an allergic reaction to antithyroid medications, according to the American Association of Clinical Endocrinologists. Symptoms include yellow skin (jaundice), skin rash, hives, fever and joint pain. This is most likely to occur within the first six weeks of treatment and usually subsides within a couple of weeks after a patient stops using the medication.

Uncommonly, antithyroid medications can damage neutrophils, a type of white blood cell that helps eradicate bacteria. Patients who use these drugs and develop a sore throat, fever or other signs of infection are urged to seek immediate medical attention so they can have a blood test performed. This should be done before the patient takes the next dose of antithyroid medication.

Thyroid drugs are among the medications that can in rare cases cause drug-induced lupus. Symptoms can include muscle and joint pain and swelling, fatigue, fever and painful inflammation around the lungs or heart. Drug-induced lupus typically resolves when the medication is discontinued. It is far less serious than systemic lupus erythematosus, a chronic autoimmune disorder.

Patients who take too much thyroid hormone may develop hyperthyroidism or other side effects, such as strain on the heart or osteoporosis. Patients who take too little are likely to experience continued hypothyroidism. In addition, patients who take thyroid hormone to try to suppress the growth of thyroid nodules or enlarged thyroid gland (goiter) may experience several side effects. These include irregular or fast heartbeat, chest pain and decreased bone density.

Radioactive iodine therapy initially causes a release of thyroid hormone into the bloodstream that may cause symptoms to worsen for a time after treatments begin. These symptoms may include neck tenderness, sore throat and signs of hyperthyroidism. However, over time they begin to reverse as the treatment takes effect.

Beta blockers can cause mild hyperglycemia in diabetic patients, and studies have found them to be a minor risk factor for diabetes. Depending on the type of beta blocker prescribed, patients may experience various side effects, such as slow heart rate (bradycardia), shortness of breath (dyspnea) or wheezing, dizziness or fainting.

Other side effects associated with thyroid medications can include:

• Anxiety
• Burning, tingling or other abnormal sensations
• Diarrhea, stomach cramps or other gastrointestinal upset
• Drowsiness
• Fever
• Flushing
• Hair loss
• Headache
• Hyperactivity
• Increased appetite (polyphagia)
• Loss of taste or salty taste
• Menstrual cycle changes
• Mouth sores or throat infection
• Muscle/joint pain or weakness
• Nausea or vomiting
• Rapid changes in mood (e.g., irritability)
• Skin rash, itchiness or eruptions
• Sleeping difficulties
• Swelling (edema)
• Tremor or shakiness
• Weight changes