Synthroid is the brand-name form of levothyroxine. They’re both prescribed for certain thyroid conditions, including hypothyroidism caused by Hashimoto disease (also called Hashimoto thyroiditis). If ...

Synthroid (levothyroxine) can interact with many medications, supplements, and foods that may make it less effective. These include antacids, calcium and iron supplements, birth control containing ...

Common side effects of levothyroxine include tremors, insomnia, heart-related problems, headache, and muscle spasms or muscle weakness. It’s possible for levothyroxine to cause long-term side effects, ...