Why the stomach matters
Most tablets are absorbed after they leave the stomach and reach the small intestine. When a GLP-1 slows that exit, a medicine can arrive later, and its peak level in the blood can be lower or come later than usual, even when the total amount absorbed is similar.
The tirzepatide and Foundayo™ labels add a detail about timing: the effect on stomach emptying was greatest after the first dose and became smaller with later doses [4][6]. The Trulicity® label says the same and adds that the delay depends on the dose, which its gradual dose steps are meant to soften [8].
What each label tested
Each manufacturer studied a short list of common oral medicines alongside its own GLP-1. The table summarises what was tested, what changed and what the US label asks in return.
| Medicine | What was tested | Main finding | What the label asks |
|---|---|---|---|
| Ozempic® injection [3] | Metformin, warfarin, digoxin, atorvastatin, a combined birth control pill (semaglutide 1 mg at steady state) | No clinically relevant change | Caution when oral medicines are taken with it |
| Rybelsus®, Ozempic® tablets, Wegovy® tablets [1][2] | Levothyroxine, warfarin, metformin, digoxin, lisinopril, furosemide, rosuvastatin, a combined pill; omeprazole | Total thyroxine exposure +33%, peak unchanged; no clinically significant change for the rest | Consider extra monitoring for narrow-margin medicines |
| Mounjaro® and Zepbound® [4][5] | Acetaminophen (paracetamol), a combined pill | Paracetamol peak 50% to 55% lower and an hour later after a first 5 mg dose; no meaningful effect at week 4 or 6 | Monitor medicines like warfarin; specific pill advice |
| Saxenda® [7] | Paracetamol, atorvastatin, digoxin, lisinopril, griseofulvin, a combined pill | Peaks 27% to 38% lower for four medicines; griseofulvin peak 37% higher | Watch for effects of delayed absorption |
| Trulicity® [8] | Several oral medicines at the 1.5 mg dose | No clinically relevant effect; limited experience at 3 mg and 4.5 mg | Monitor drug levels of narrow-margin medicines such as warfarin |
| Foundayo™ [6] | Enzyme blockers and inducers, statins, digoxin, paracetamol | Several clinically relevant changes (see below); paracetamol peak 28% lower after the first dose | Dose cap, medicines to avoid and a simvastatin ceiling |
Semaglutide tablets: a window that works both ways
Semaglutide tablets come with their own routine. The labels describe taking one in the morning on an empty stomach with a little plain water, up to 4 ounces, then letting at least half an hour pass before eating, drinking or swallowing another medicine [1][2]. The European product information also asks for a fast of at least 8 hours beforehand and caps the water at half a glass, about 120 mL [9].
The wait protects the semaglutide as much as the other medicine. In the European and Canadian documents, taking semaglutide together with five other tablets lowered its total exposure by 34% and its peak by 32%, which they attribute to several tablets sitting in the stomach at once [9][11]. A published pharmacology study found little or no measurable semaglutide when a meal came 30 minutes before the dose, and higher exposure with longer fasting after it; 50 mL and 120 mL of water made no clear difference [12].
If you take several morning medicines, plan the order and timing with your pharmacist rather than adjusting them on your own.
Levothyroxine and thyroid tests
In an interaction study, a single dose of levothyroxine, a thyroid hormone, was taken with semaglutide tablets. Total thyroxine exposure, corrected for the body’s own hormone, was 33% higher, while its peak level did not change [1][2]. The US labels respond by suggesting closer clinical or laboratory monitoring for medicines like this; the European product information says monitoring of thyroid values should be considered [1][9].
The injectable semaglutide label reports no such signal, because levothyroxine was not among the medicines it tested [3]. Whether your thyroid tests or the timing of your thyroid tablet should change is a question for your prescriber.
Warfarin and other narrow-margin medicines
Some medicines work only within a tight range of blood levels; the labels call this a narrow therapeutic index. The Mounjaro®, Zepbound® and Trulicity® labels name warfarin as the example and ask for monitoring when it is taken alongside them [4][5][8].
For semaglutide tablets, warfarin levels themselves did not change in the study [1]. The European product information goes further: it notes reports of lower INR, the clotting test used for these medicines, with acenocoumarol, a related blood thinner, and recommends frequent INR checks when semaglutide is started in someone already taking warfarin or a similar medicine [9][10].
Tirzepatide: what the studies measured
The Mounjaro® and Zepbound® labels describe a test with acetaminophen (paracetamol), which the labels use as a marker of stomach emptying. After a first 5 mg dose of tirzepatide, its peak level fell by 50% in one label and 55% in the other, and the peak came about an hour later [4][5]. Weeks later, with continued treatment, there was no meaningful effect, and total exposure did not change.
Both labels ask for caution with oral medicines and for monitoring of medicines that depend on reaching a certain blood level to work, or that have a narrow therapeutic index. Warfarin is the example they give.
Birth control pills: a separate rule
Hormonal pills are the one group for which the tirzepatide and Foundayo™ labels give specific advice. For a set period after starting, and again after every step up, the labels point pill users to a contraceptive that is not swallowed, or to a condom alongside the pill [4][6]. The window is four weeks for tirzepatide and 30 days for Foundayo™. Contraceptives that are not taken by mouth are not expected to be affected. The full details are in our article on GLP-1s and birth control pills.
Liraglutide: small timing changes
The Saxenda® label says liraglutide did not change absorption of the tested medicines to a clinically relevant degree, and asks prescribers to watch for consequences of delayed absorption [7]. Its pharmacology section shows lower peak levels for several medicines: acetaminophen by 31%, atorvastatin by 38%, digoxin by 31% and lisinopril by 27%. Griseofulvin, an antifungal, went the other way, with a 37% higher peak.
MedlinePlus lists acetaminophen (Tylenol®) as a nonprescription product that may interact with liraglutide and asks you to let your doctor and pharmacist know if you take it [13].
Foundayo: a different kind of interaction
Foundayo™ (orforglipron) is a daily tablet, and its label adds interactions that the injectable labels do not have. Orforglipron is processed by a liver enzyme called CYP3A4. Strong blockers of that enzyme raise its levels; clarithromycin, for example, increased exposure 3.5-fold. The label limits the Foundayo™ dose to 9 mg a day when a strong CYP3A4 blocker is used, and says to avoid strong blockers that also act on a liver transporter, ritonavir being the example [6].
Inducers work in the opposite direction. Carbamazepine lowered orforglipron exposure by 82%, so strong inducers are to be avoided; with moderate inducers the label asks prescribers to watch whether the medicine is still working. An acid-reducing medicine, esomeprazole, had no effect [6].
It works the other way too. Foundayo™ doubled exposure to the active form of simvastatin, a cholesterol medicine, so the label sets a ceiling of 20 mg a day for simvastatin taken with it. Atorvastatin and rosuvastatin levels also rose, but the label does not regard those changes as clinically relevant [6].
Insulin and sulfonylureas
Most of the labels also list insulin and sulfonylureas, medicines that make the pancreas release insulin, as an interaction. Used together with a GLP-1, they raise the risk of low blood sugar, and the labels suggest prescribers consider lowering their dose when the GLP-1 is started [1][4][6]. That concerns blood sugar rather than absorption.
Keeping your medicine list in one place
MedlinePlus asks people to tell their doctor and pharmacist about every prescription and nonprescription medicine, vitamin, supplement and herbal product, because doses may need changing or side effects may need watching [14]. The Medication Guide for semaglutide tablets suggests keeping a written list to show them whenever a new medicine is added [1].
Bring that list to each new prescriber, including dentists and surgeons. The labels also ask you to mention a GLP-1 before any planned procedure with anaesthesia, because a slow-emptying stomach matters there too [1][6].
Ozempic®, Wegovy®, Rybelsus® and Saxenda® are registered trademarks of Novo Nordisk A/S. Mounjaro®, Zepbound® and Trulicity® are registered trademarks and Foundayo™ is a trademark of Eli Lilly and Company. Tylenol® is a registered trademark of its owner. PepLabo is not affiliated with or endorsed by Novo Nordisk, Eli Lilly or the owner of Tylenol®.
When to get help
The signs and contact information below come from this article’s sourced guidance.
Emergency
- You took more semaglutide tablets than prescribed
Contact: Poison Help line or emergency department
Rybelsus® and Ozempic® tablets Medication Guide [1]
Today
At your next appointment
- Starting a GLP-1 while on warfarin, a thyroid tablet or another medicine that needs blood tests
Contact: Your prescriber or pharmacist, to plan monitoring
- A new prescription, supplement or planned procedure while on a GLP-1
Contact: Your pharmacist and the clinician involved