GLP-1 drug interactions: what the labels say

Weekly GLP-1 medications slow how fast your stomach empties, and that can change how other pills are absorbed. Here is what the official US prescribing information and Canadian product monographs say about birth control, insulin, thyroid medication and other oral drugs. Your prescriber's and pharmacist's advice comes first.

Interactions at a glance

Why oral medications are affected

Every one of these labels lists delayed gastric emptying as the reason for its drug interaction warnings. When food and pills sit in the stomach longer, an oral medication can reach the bloodstream later or in a different amount. The labels ask prescribers to use caution with oral medications in general, and to watch more closely the ones that only work within a narrow range in the blood.

The Mounjaro and Zepbound labels name warfarin as an example of a narrow-therapeutic-index drug to monitor. The Wegovy label recommends more clinical or laboratory monitoring for oral medications with a narrow therapeutic index or that need clinical monitoring. The Ozempic label notes that in clinical pharmacology trials semaglutide did not affect the absorption of the oral medications studied to any clinically relevant degree, but still asks for caution.

Birth control pills and tirzepatide

This is the interaction people most often miss. The US Mounjaro and Zepbound labels, and Health Canada's Mounjaro product monograph, advise anyone using oral hormonal contraceptives to switch to a non-oral method or add a barrier method (such as condoms) for 4 weeks after starting, and for 4 weeks after each dose increase. The labels say hormonal contraceptives that are not taken by mouth should not be affected.

The Canadian monograph explains why: in a clinical study, a single tirzepatide dose lowered the peak level of an oral contraceptive by 55 to 66%, lowered total exposure by 16 to 23%, and delayed the peak by 2.5 to 4.5 hours. The monograph also recommends contraception for women of childbearing potential, as Mounjaro is contraindicated in pregnancy in Canada.

Because the 4-week window restarts with every dose step, it helps to log the date of each dose increase. That way you can see exactly when each backup window ends.

Birth control pills and semaglutide

The Ozempic label's clinical pharmacology data include an oral contraceptive (ethinylestradiol/levonorgestrel) studied at steady state, and the label reports no clinically relevant effect on absorption. Neither the Ozempic nor Wegovy label carries the 4-week backup advice. Both labels do say to stop semaglutide at least 2 months before a planned pregnancy because of its long washout period, so talk to your prescriber if you are planning a pregnancy.

Insulin and sulfonylureas

GLP-1 medications lower blood sugar. All four labels warn that using them with insulin or an insulin secretagogue such as a sulfonylurea raises the risk of hypoglycemia, and the Ozempic label says this includes severe hypoglycemia. The labels tell prescribers to consider reducing the insulin or sulfonylurea dose when the GLP-1 is started. Never adjust these doses yourself. If you use insulin or a sulfonylurea, ask your care team what low blood sugar symptoms to watch for and what to do.

Levothyroxine and other monitored drugs

The US Wegovy label reports that in a drug interaction study with the semaglutide tablet, levothyroxine exposure increased by 33%. It recommends monitoring the effects of oral medications taken with Wegovy. If you take thyroid medication, a blood thinner such as warfarin, or another drug that needs regular blood tests, ask your prescriber whether to check levels after you start or change your GLP-1 dose.

A simple checklist for appointments

• Bring a full list of what you take, including over-the-counter drugs, vitamins and supplements.
• Say whether you use birth control pills, insulin, a sulfonylurea, thyroid medication or a blood thinner.
• Note the dates you started and each time your GLP-1 dose changed (see the dose schedule guide for the label steps).
• Record stomach side effects such as vomiting or diarrhea, which can also affect how pills are absorbed (see tracking side effects).
• Tell any surgeon or anesthetist that you take a GLP-1 medication.

Sources

• Ozempic prescribing information, sections 7, 8.3 and 12.3 (DailyMed, US)
• Wegovy prescribing information, section 7 (DailyMed, US)
• Mounjaro prescribing information, sections 7 and 8.3 (DailyMed, US)
• Zepbound prescribing information, sections 7 and 8.3 (DailyMed, US)
• Mounjaro product monograph, sections 7 and 9.4 (Eli Lilly Canada)
• Ozempic product monograph (Novo Nordisk Canada)

This page summarizes official product labels as general information. It is not medical advice and is not a complete list of interactions. Do not start, stop or change any medication without talking to your prescriber or pharmacist. Labels are updated; check the current version for your product.

Frequently asked questions