Every GLP-1 medicine slows the stomach, and that is the interaction all of their labels share: other pills taken at the same time may be absorbed later or less completely. Beyond that shared line, the labels differ more than most summaries say. Only the two tirzepatide labels and Foundayo tell prescribers to switch people off oral birth control, or add a barrier method, for a few weeks after each dose step. The semaglutide labels carry no such instruction, but report a 33% rise in levothyroxine exposure. Foundayo, the newest, is the only one with liver-enzyme interactions.
This page reads section 7 (Drug Interactions) and the interaction studies in section 12.3 of seven US labels, all opened on DailyMed on 2 November 2026. It reports what each label states. It does not advise anyone to start, stop or change a medicine; that is a prescriber's decision, made with the full medication list.
The labels read
| Label (molecule) | Version read | Insulin / sulfonylurea line | Oral medicines line | Contraception line |
|---|---|---|---|---|
| Zepbound (tirzepatide) | effective 28 Aug 2026 | yes | yes, warfarin named | yes, 4 weeks |
| Mounjaro (tirzepatide) | effective 27 Aug 2026 | yes | yes, warfarin named | yes, 4 weeks |
| Foundayo (orforglipron) | effective 29 Jul 2026 | yes | yes, plus enzyme interactions | yes, 30 days |
| Wegovy (semaglutide, injection and tablets) | effective 18 Jun 2026 | yes | yes, levothyroxine +33% | none |
| Ozempic (semaglutide injection) | effective 1 Jun 2026 | yes | yes | none |
| Rybelsus / Ozempic tablets (oral semaglutide) | effective 30 Jan 2026 | yes | yes, levothyroxine +33% | none |
| Saxenda (liraglutide) | effective 25 Feb 2026 | not in section 7 | yes | none |
Saxenda's section 7 contains only the oral-medicines paragraph; low blood sugar with diabetes medicines is handled elsewhere in its label. The table records where each line sits, not how important it is.
The interaction they all share: a slower stomach
Each label states that the drug "delays gastric emptying" and so "has the potential to impact the absorption of concomitantly administered oral medications". What they ask prescribers to do about it varies in wording:
- Zepbound and Mounjaro: "Caution should be exercised", and monitor people on oral drugs "dependent on threshold concentrations for efficacy and those with a narrow therapeutic index (e.g., warfarin)".
- Wegovy and Rybelsus: "consider increased clinical or laboratory monitoring" for oral drugs "that have a narrow therapeutic index or that require clinical monitoring".
- Ozempic and Saxenda: "Use with caution"; Saxenda adds monitoring "for potential consequences of delayed absorption".
The effect is largest at the start. The Zepbound label puts a number on it: after a first 5 mg dose, the peak level of acetaminophen (paracetamol, used in these studies as a marker of stomach emptying) fell by 55% and arrived an hour later. By week 6, on 15 mg, the label found "no meaningful impact" on acetaminophen's peak or timing, and total exposure was not changed at either point. That fading pattern is why the tirzepatide contraception instruction is tied to the first weeks after each dose step, rather than to the whole course.
The semaglutide labels describe the same mechanism but report that in their clinical-pharmacology trials semaglutide "did not affect the absorption of orally administered medications" to any clinically relevant degree, while still asking for caution.
Insulin and sulfonylureas: the low-blood-sugar line
GLP-1 medicines lower blood glucose by raising insulin release when glucose is high. On their own, the labels report low rates of hypoglycaemia. Combined with drugs that push insulin up regardless of glucose, the risk rises. Six of the seven labels say so in section 7:
"When initiating ZEPBOUND, consider reducing the dose of concomitantly administered insulin or insulin secretagogues (e.g., sulfonylureas) to reduce the risk of hypoglycemia." — Zepbound label, 7.1
The Ozempic label adds "including severe hypoglycemia". The Wegovy label notes that "the addition of WEGOVY in patients treated with insulin has not been evaluated". Sulfonylureas include glipizide, glimepiride and glyburide. The labels leave the size of any dose change to the prescriber. People with type 2 diabetes who also take a GLP-1 are the group this applies to; this site's page on Ozempic for type 2 diabetes covers that use.
Birth-control pills: a tirzepatide and Foundayo instruction
This is the line most often reported wrongly. It is not on every GLP-1 label.
The Zepbound and Mounjaro labels state that tirzepatide "may reduce the efficacy of oral hormonal contraceptives due to delayed gastric emptying", that "this delay is largest after the first dose and diminishes over time", and instruct:
"Advise patients using oral hormonal contraceptives to switch to a non-oral contraceptive method, or add a barrier method of contraception for 4 weeks after initiation with ZEPBOUND and for 4 weeks after each dose escalation. Hormonal contraceptives that are not administered orally should not be affected." — Zepbound label, 7.2 and 8.3
The figures behind it, from the Zepbound label's section 12.3, after a single 5 mg dose given with a combined pill (0.035 mg ethinyl estradiol and 0.25 mg norgestimate):
| Hormone | Peak level (Cmax) | Total exposure (AUC) |
|---|---|---|
| Ethinyl estradiol | −59% | −20% |
| Norgestimate | −66% | −21% |
| Norelgestromin (metabolite) | −55% | −23% |
The time to peak was delayed by 2.5 to 4.5 hours. The study measured one dose; the label does not report the same measurement after later doses, and it does not report pregnancies attributed to the interaction. Those are the limits of the record.
Foundayo carries the same instruction with a different period: "for 30 days after initiation with FOUNDAYO and for 30 days after each dose escalation" (label 7.3).
The semaglutide labels carry no contraception instruction. The Wegovy label's interaction studies list ethinyl estradiol and levonorgestrel among the drugs with "no clinically significant differences" in levels when taken with semaglutide. A pill-and-injection user moving between molecules meets two different instructions, which is why the question belongs with the prescriber, who has the label for the specific product. The GLP-1 labels' separate pregnancy guidance is on GLP-1s and pregnancy.
Levothyroxine: the semaglutide-tablet number
Both semaglutide labels that cover tablets (Wegovy and Rybelsus) report the same study: total thyroxine exposure rose 33% (90% confidence interval 1.25 to 1.42) after a single 600 mcg levothyroxine dose taken with oral semaglutide; the peak level was unchanged. The labels do not call this a contraindication. They ask for more clinical or laboratory monitoring of oral drugs with a narrow therapeutic index or that need monitoring, which describes thyroid replacement.
The tablet labels also set a timing rule that affects every other morning pill. The Rybelsus label sets the tablet's use "on an empty stomach in the morning with water (up to 4 ounces of water)", followed by a wait of "at least 30 minutes before eating food, drinking beverages or taking other oral medications". That is an instruction for the tablet's own absorption, not a finding about any second drug. The oral options are compared on GLP-1 pill vs injection.
What the semaglutide studies found no clinically significant change in: lisinopril, S- and R-warfarin, metformin, digoxin, ethinyl estradiol, levonorgestrel, furosemide and rosuvastatin; omeprazole did not change semaglutide's own levels.
Foundayo: the only enzyme interactions in the class
The peptide GLP-1s are broken down like proteins and have, in their labels' words, "very low potential" or "low potential" to inhibit or induce liver enzymes. Orforglipron is a small molecule, and its label is the first in the class with interactions of the ordinary drug-metabolism kind:
| Combined with | Foundayo label instruction (section 7) | Reason given |
|---|---|---|
| Strong CYP3A4 inhibitors | maximum Foundayo 9 mg once daily | inhibitors raise orforglipron exposure |
| Strong CYP3A4 inhibitors that also inhibit OATP1B (e.g. ritonavir) | avoid | "expected to significantly increase" orforglipron levels |
| Strong CYP3A4 inducers | avoid | lower orforglipron exposure, may reduce effect |
| Moderate CYP3A4 inducers | monitor effectiveness | lower exposure |
| Simvastatin | do not exceed 20 mg once daily | orforglipron doubled simvastatin acid exposure |
Common strong CYP3A4 inhibitors include some antifungals and HIV and hepatitis C medicines; common inducers include rifampicin and some anti-seizure drugs. The label's own tables are the reference; this list is illustrative, not complete. Foundayo's price and trial figures are on the Foundayo vs Wegovy pill comparison.
Procedures under anaesthesia
A slow stomach matters for one more thing that is not a drug: sedation. The Zepbound label's warning 5.9 records "rare postmarketing reports of pulmonary aspiration" in people on GLP-1 receptor agonists who had food left in the stomach despite fasting as instructed, and states that "available data are insufficient to inform recommendations" on whether pausing the drug or changing fasting rules reduces the risk. It instructs patients to tell their healthcare providers before any planned surgery or procedure. What the anaesthesia societies have published since is on GLP-1s and surgery.
What the labels do not cover
- Antidepressants, ADHD medicines, antibiotics, blood-pressure tablets other than lisinopril: none is named in section 7 of any of the seven labels. The general oral-absorption line applies to all of them, and nothing more specific is published there.
- Alcohol is not a drug interaction in these labels; what the trials and studies report is on GLP-1s and alcohol.
- Supplements marketed alongside GLP-1s are not studied in any label.
- Compounded semaglutide or tirzepatide has no FDA label of its own, so none of these interaction studies was run on those products.
Absence from a label means the manufacturer did not list it, not that a combination has been shown safe. The full medication list, including over-the-counter products, is what a prescriber or pharmacist checks.
Sources
- US prescribing information on DailyMed, each opened 2 November 2026: Zepbound (effective 28 Aug 2026), Mounjaro (27 Aug 2026), Foundayo (29 Jul 2026), Wegovy (18 Jun 2026), Ozempic (1 Jun 2026), Rybelsus and Ozempic tablets (30 Jan 2026), Saxenda (25 Feb 2026). Sections 2.1, 5.9, 7, 8.3, 12.2 and 12.3 as cited above.
- The class overview of side effects is on GLP-1 side effects; how these drugs act on the stomach is on how GLP-1s work.