Interaction reference
GLP-1 receptor agonists with Levothyroxine
Levothyroxine absorption is sensitive to gastric emptying timing. GLP-1s delay gastric emptying, which can reduce levothyroxine bioavailability.
Take levothyroxine at least 60 minutes before any GLP-1 dose. Recheck TSH at 6-8 weeks after starting a GLP-1.
Also known as: Synthroid, Levoxyl, Unithroid
Per-GLP-1 breakdown
- Wegovysemaglutide 2.4 mgModerate
Mechanism: Delayed gastric emptying reduces levothyroxine Cmax and bioavailability, particularly when both are taken in the morning.
What to do: Take levothyroxine 60+ minutes before breakfast and any GLP-1 dose. Recheck TSH 6-8 weeks after starting the GLP-1 and after each dose escalation. Adjust levothyroxine dose only on the basis of TSH change, not symptoms.
- ZepboundtirzepatideModerate
Mechanism: Delayed gastric emptying reduces levothyroxine Cmax and bioavailability, particularly when both are taken in the morning.
What to do: Take levothyroxine 60+ minutes before breakfast and any GLP-1 dose. Recheck TSH 6-8 weeks after starting the GLP-1 and after each dose escalation. Adjust levothyroxine dose only on the basis of TSH change, not symptoms.
- OzempicsemaglutideModerate
Mechanism: Delayed gastric emptying reduces levothyroxine Cmax and bioavailability, particularly when both are taken in the morning.
What to do: Take levothyroxine 60+ minutes before breakfast and any GLP-1 dose. Recheck TSH 6-8 weeks after starting the GLP-1 and after each dose escalation. Adjust levothyroxine dose only on the basis of TSH change, not symptoms.
- MounjarotirzepatideModerate
Mechanism: Delayed gastric emptying reduces levothyroxine Cmax and bioavailability, particularly when both are taken in the morning.
What to do: Take levothyroxine 60+ minutes before breakfast and any GLP-1 dose. Recheck TSH 6-8 weeks after starting the GLP-1 and after each dose escalation. Adjust levothyroxine dose only on the basis of TSH change, not symptoms.
- FoundayoorforglipronModerate
Mechanism: Delayed gastric emptying reduces levothyroxine Cmax and bioavailability, particularly when both are taken in the morning.
What to do: Take levothyroxine 60+ minutes before breakfast and any GLP-1 dose. Recheck TSH 6-8 weeks after starting the GLP-1 and after each dose escalation. Adjust levothyroxine dose only on the basis of TSH change, not symptoms.