How to read the severity tiers
- Contraindicated — Do not combine. The combination is either explicitly contraindicated by the FDA label or universally recognized as unsafe (e.g., two GLP-1 receptor agonists at the same time).
- Serious — Combination is allowed but requires close monitoring or proactive dose adjustment of one of the drugs. The classic example is insulin or a sulfonylurea — both can cause hypoglycemia, and adding a GLP-1 on top requires reducing the dose of the existing diabetes medication before the first GLP-1 dose.
- Moderate — Be aware. The interaction is real but usually does not require dose adjustment. Often involves slowed gastric emptying affecting the absorption rate (not total bioavailability) of an oral medication. Examples: warfarin, levothyroxine, oral contraceptives.
- Minor — Generally no action needed. Either no documented interaction or the effect is clinically irrelevant (e.g., a 30-60 minute delay in acetaminophen onset).
Why GLP-1s have so many gastric-emptying interactions
GLP-1 receptor agonists slow gastric emptying as part of their mechanism of action — that's a major contributor to the satiety effect that produces weight loss. The same mechanism delays the absorption of orally administered medications by 30-60 minutes on average. For most drugs, total bioavailability (the area under the curve, AUC) is preserved, so the drug still works, but it may take slightly longer to reach peak concentration. The clinical significance is small for most medications and meaningful only for drugs with a narrow therapeutic window or a time-sensitive onset.
Hypoglycemia risk with insulin and sulfonylureas
The most clinically important GLP-1 interaction is the additive hypoglycemia risk when combined with insulin or a sulfonylurea (glipizide, glyburide, glimepiride). GLP-1s enhance glucose-dependent insulin secretion — meaning they only push insulin when blood sugar is elevated — but adding insulin or a sulfonylurea on top can produce dangerous lows. The standard protocol is to reduce the insulin dose by approximately 20% (or taper off the sulfonylurea) BEFORE the first GLP-1 dose. This should be discussed with your prescriber in advance, not after the fact.
Oral contraceptives and Foundayo
Foundayo (orforglipron, the new oral GLP-1 approved April 2026) carries a more specific drug interaction warning for oral contraceptives than the injectable GLP-1s. The Foundayo label recommends backup contraception (barrier, IUD, implant, or non-oral hormonal) for 30 days after starting the drug and 30 days after each dose increase. Women on oral birth control who plan to start any GLP-1 should discuss a backup contraception strategy with their prescriber.
What this tool is NOT
This is an educational lookup tool, not a clinical decision support system. It is not a substitute for your prescriber, your pharmacist, or a real-time interaction checker built into electronic health records. The database covers the highest-frequency clinically meaningful interactions but is not exhaustive. Always tell every prescriber and pharmacist about every medication you take, including over-the-counter products and supplements, and confirm any specific interaction with them before starting or stopping anything.
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Important disclaimer
This tool is for educational purposes only and does not constitute medical advice. Drug interactions are highly individual and depend on dose, timing, and your overall medication list. Weight Loss Rankings does not provide medical advice, diagnosis, or treatment recommendations. Always consult your prescribing clinician and pharmacist before combining any medication with a GLP-1 receptor agonist.