What medications, foods, or supplements should be avoided for a patient on Synthroid (levothyroxine)?

Medications, Foods, and Supplements to Avoid with Levothyroxine (Synthroid)

Patients on levothyroxine should separate their medication from interfering substances by at least 4 hours to ensure optimal absorption and therapeutic efficacy. 1

Timing of Administration

• Take levothyroxine as a single daily dose on an empty stomach
• Administer 30-60 minutes before breakfast with a full glass of water
• Maintain consistent timing each day to ensure stable hormone levels

Medications to Avoid Taking Within 4 Hours of Levothyroxine

High Priority Interactions

• Calcium supplements (carbonate, citrate, acetate) - significantly reduce absorption 2, 1
• Iron supplements/ferrous sulfate - form insoluble complexes with levothyroxine 1, 3
• Antacids containing aluminum hydroxide - bind to levothyroxine 3
• Bile acid sequestrants (cholestyramine, colestipol, colesevelam) - strongly bind levothyroxine 2, 3
• Phosphate binders (sevelamer, lanthanum) - reduce absorption 3, 4

Other Medication Interactions

• Proton pump inhibitors - alter gastric pH affecting dissolution 3, 5
• Sucralfate - forms complexes with levothyroxine 3
• Ciprofloxacin and other fluoroquinolones - chelate with levothyroxine 3
• Orlistat - may affect absorption through fat malabsorption 3
• Raloxifene - potential binding interaction 3

Foods and Beverages to Avoid Within 4 Hours

• Coffee/espresso - significantly reduces absorption even when taken 60 minutes after levothyroxine 6, 7
• Soy products - interfere with absorption and may affect thyroid function 6, 7
• High-fiber foods - may bind to levothyroxine in the digestive tract 6, 7
• Milk and dairy products - calcium content can reduce absorption 6
• Grapefruit juice - may affect metabolism of levothyroxine 5

Supplements to Avoid Within 4 Hours

• Chromium supplements - significantly decrease levothyroxine absorption 4
• Multivitamins containing iron or calcium - same binding issues as individual supplements 1
• Vitamin C - interestingly, can actually enhance absorption, but timing should still be separated 6

Clinical Recommendations

1. Medication Schedule Planning:

   • Morning: Take levothyroxine first thing, wait at least 30-60 minutes before breakfast
   • Evening: Take interfering medications/supplements
   • Alternative: Consider bedtime dosing of levothyroxine if consistent timing can be maintained

2. Monitoring Protocol:

   • Check TSH and free T4 levels 6-8 weeks after starting any new medication
   • Monitor for symptoms of hypothyroidism if new medications are added
   • Consider more frequent monitoring when multiple interacting substances are used

3. Patient Education:

   • Explain that absorption issues can lead to inadequate treatment
   • Emphasize the importance of consistent timing and separation of doses
   • Advise patients to inform all healthcare providers about levothyroxine use

Special Considerations

• For patients with multiple medications, create a specific schedule to maximize absorption
• Liquid levothyroxine formulations may be less affected by some food interactions
• Patients with gastrointestinal disorders (celiac disease, H. pylori infection, atrophic gastritis) may need closer monitoring due to potential absorption issues 3, 7

Remember that consistent administration timing and proper separation from interfering substances are crucial for maintaining stable thyroid hormone levels and avoiding fluctuations in thyroid function.