Drug Interactions Between Levothyroxine and Bupropion (Wellbutrin)
There are no significant direct pharmacokinetic interactions between levothyroxine and bupropion (Wellbutrin), but proper administration timing is recommended to avoid potential absorption issues with levothyroxine.
Key Considerations
Levothyroxine has a narrow therapeutic index and is susceptible to absorption interactions with many substances, though bupropion is not specifically identified as a direct interactor 1, 2
The primary concern is maintaining optimal levothyroxine absorption, which can be affected by the timing of medication administration 3, 2
Patients taking both medications should separate administration times by at least 1 hour before or 4-6 hours after taking levothyroxine to minimize any potential absorption interference 3
Levothyroxine Absorption Considerations
Levothyroxine is administered in small amounts (micrograms) with a narrow therapeutic index, making any absorption interference potentially clinically significant 2
While bupropion is not specifically documented to interfere with levothyroxine absorption, as a general precaution, separating administration times is recommended 3, 2
Monitoring thyroid function (TSH levels) is important when starting or adjusting either medication to ensure optimal therapeutic effect 3, 4
Bupropion Considerations
Bupropion commonly causes side effects including dry mouth, insomnia, headache, dizziness, nausea, constipation, and tremor 5
The most serious potential adverse effect of bupropion is seizures (rate of 1/1000), which requires careful patient screening and dosage adherence 5
Bupropion should be used with caution in patients with cardiovascular disease, as it can cause cardiovascular effects including tachycardia 5
Monitoring Recommendations
Monitor thyroid function (TSH levels) when starting bupropion in patients already on levothyroxine therapy to ensure continued efficacy of thyroid replacement 3, 6
Watch for signs of hypothyroidism (fatigue, cold intolerance, weight gain) or hyperthyroidism (nervousness, palpitations, heat intolerance) which could indicate a need for levothyroxine dose adjustment 3, 4
Monitor blood pressure and heart rate periodically while taking bupropion, especially during the first 12 weeks of treatment 5
Administration Guidelines
Take levothyroxine on an empty stomach, 30-60 minutes before breakfast 2, 7
Administer bupropion at least 1 hour after or 4-6 hours before levothyroxine to minimize any potential absorption interference 3
Maintain consistent timing of both medications to ensure stable blood levels and therapeutic effect 6, 2
Special Situations
If a patient shows unexpected changes in thyroid function after starting bupropion, consider evaluating the administration schedule and potentially adjusting the timing of medications 6
Patients with thyroid disease who are starting bupropion should be monitored more closely during the initial treatment period 5, 6
If absorption issues are suspected despite proper timing, consider checking TSH levels and adjusting levothyroxine dosage as needed 6, 2