After taking levothyroxine (Synthroid) at 6 a.m., when can I take my clonazepam and losartan?

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Last updated: September 11, 2026 • View editorial policy

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Timing of Clonazepam and Losartan After Morning Synthroid

You can take your clonazepam and losartan immediately at 6 a.m. with your Synthroid, as neither medication interferes with levothyroxine absorption.

Key Timing Principles for Levothyroxine

The FDA label for Synthroid clearly states that levothyroxine should be taken at least 4 hours apart from drugs that are known to interfere with its absorption 1. The critical point here is that this separation only applies to medications that actually interfere with absorption.

Medications That DO Require Separation

Based on the FDA labeling and clinical guidelines, you need to wait at least 4 hours after Synthroid before taking 1:

  • Iron supplements
  • Calcium supplements
  • Antacids
  • Proton pump inhibitors (like omeprazole, pantoprazole)

Research confirms these interactions are clinically significant, with iron, calcium, and proton pump inhibitors increasing TSH levels by 0.12-0.27 mIU/L and causing TSH increases >5 mIU/L in 4-8% of patients 2.

Why Clonazepam and Losartan Are Safe to Take Together

Neither clonazepam (a benzodiazepine) nor losartan (an angiotensin receptor blocker) appear on the list of medications that interfere with levothyroxine absorption. The FDA label specifically mentions agents like iron, calcium, and antacids as requiring separation 1, but does not include benzodiazepines or ARBs.

Optimal Administration Strategy

For your specific situation:

  • Take Synthroid at 6 a.m. on an empty stomach with water
  • Take clonazepam and losartan at the same time (6 a.m.)
  • Wait 30-60 minutes before eating breakfast 3

The guideline recommendation is to take levothyroxine "consistently 30-60 minutes before breakfast" 3, which optimizes absorption while maintaining compliance 3.

Important Caveats

If you are taking any of these medications, they MUST be separated by 4 hours from Synthroid:

  • Proton pump inhibitors (omeprazole, esomeprazole, pantoprazole)
  • Iron supplements
  • Calcium supplements
  • Multivitamins containing iron or calcium
  • Antacids

The concomitant use of levothyroxine with interacting drugs occurs in approximately 24% of patient visits, with 80% being proton pump inhibitors 4. This is a common pitfall that can lead to inadequate thyroid hormone replacement.

Monitor your TSH levels 4-8 weeks after starting any new medication to ensure your Synthroid dose remains adequate 1.

References

3
Guideline

clinical practice guidelines for hypothyroidism in adults: cosponsored by the american association of clinical endocrinologists and the american thyroid association.

Endocrine practice : official journal of the American College of Endocrinology and the American Association of Clinical Endocrinologist, 2012

4
Research

Concomitant use of levothyroxine and interacting medications in U.S. ambulatory care visits.

Journal of the American Pharmacists Association : JAPhA, 2023

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.