MAJOR — Use With Caution
🔴 CAUTION — Major interaction between Iron and Levothyroxine. Avoid unless under direct medical supervision.
Evidence level: STRONG
Iron supplements block thyroid medication absorption. Take at least 4 hours apart or Synthroid won't work properly.
Iron chelates levothyroxine in GI tract forming insoluble complexes. Reduces thyroid hormone absorption by up to 75%.
If you must take both, separate them by at least 4 hours. Take Iron on an empty stomach and Levothyroxine with food, or vice versa.
Take levothyroxine on an empty stomach, 30-60 minutes before breakfast. Take supplements at least 4 hours later to be safe.
Higher risk with: recently adjusted thyroid dose, autoimmune thyroid disease, pregnancy, significant dietary changes.
Your medication may not be working properly. For antibiotics: infection not improving. For thyroid meds: fatigue, weight gain, cold sensitivity returning.
Ask your doctor: "Is there a safer alternative to Iron that I can take with Levothyroxine?" Bring a list of ALL supplements and medications you take.
Thyroid medications are sensitive to absorption interference. Take levothyroxine on an empty stomach, 30-60 minutes before food or other supplements. Space calcium, iron, and antacids at least 4 hours away. Selenium and zinc are generally safe thyroid-supporting nutrients.
Iron supplements block thyroid medication absorption. Take at least 4 hours apart or Synthroid won't work properly.
Take levothyroxine on an empty stomach, 30-60 minutes before breakfast. Take supplements at least 4 hours later to be safe.
Your medication may not be working properly. For antibiotics: infection not improving. For thyroid meds: fatigue, weight gain, cold sensitivity returning.
Thyroid medications are sensitive to absorption interference. Take levothyroxine on an empty stomach, 30-60 minutes before food or other supplements. Space calcium, iron, and antacids at least 4 hours away. Selenium and zinc are generally safe thyroid-supporting nutrients.
Ask your doctor: "Is there a safer alternative to Iron that I can take with Levothyroxine?" Bring a list of ALL supplements and medications you take.
Or browse the full interaction database (121,000+ pairs).