Mounjaro interactions: birth control, insulin, alcohol and more

Mounjaro and metformin are commonly used together. The label lists no interaction between them, and three of the pivotal trials added Mounjaro to metformin: SURPASS-2 (metformin alone), SURPASS-3 (metformin with or without an SGLT2 inhibitor) and SURPASS-4, where 95% were on metformin.

In SURPASS-2, adding Mounjaro 5, 10 or 15 mg to metformin lowered HbA1c by 2.0 to 2.3 points over 40 weeks. In SURPASS-1, where Mounjaro was used without metformin or other glucose-lowering drugs, no one on Mounjaro had a reading below 54 mg/dL.

Mounjaro's own nausea and diarrhea rates are on the side effects page; if stomach symptoms continue past the first weeks of a dose, raise them with your prescriber. More on metformin itself is on our metformin page.

The label's interaction section names one main concern: low blood sugar when Mounjaro is added to insulin or an insulin secretagogue such as a sulfonylurea.

• With basal insulin (SURPASS-5), 14% to 19% on Mounjaro had glucose below 54 mg/dL over 40 weeks, against 13% on placebo, and up to 2% had severe episodes.
• With a sulfonylurea, up to 13.8% had readings under 54 mg/dL over as long as 104 weeks.

The label tells prescribers to consider lowering the insulin or sulfonylurea dose when Mounjaro starts. Do not change those doses on your own. Ask: "Should my insulin or glipizide dose change when I start Mounjaro, and what reading should make me call?" Lilly's FAQ notes Mounjaro was studied with a range of diabetes medicines.

Tirzepatide slows how fast the stomach empties, which can change how quickly pills are absorbed. The effect is largest after the first dose and fades with later ones.

Birth control pills are the case the label singles out. In a study, a single 5 mg dose cut peak levels of ethinyl estradiol by 59% and norgestimate by 66%, and total exposure by about 20%. So for anyone on an oral hormonal contraceptive, the label recommends changing to a contraceptive that is not swallowed, or using condoms as well, for 4 weeks after the first dose and 4 weeks after every dose increase. Patches, rings, implants, injections and IUDs are not expected to be affected.

For drugs with a narrow margin, such as warfarin, the label asks for monitoring.

The Mounjaro label does not list alcohol as an interaction, and it gives no drinking limit. The practical concern is blood sugar. The American Diabetes Association warns that alcohol combined with insulin or a sulfonylurea can cause hypoglycemia, because the liver prioritizes clearing alcohol over releasing glucose, especially when drinking without food. Lows can also arrive hours after the last drink, and their symptoms can be mistaken for being drunk.

Alcohol may also add to nausea or stomach upset during dose increases, when Mounjaro's gut effects peak. If you drink, the ADA suggests eating while you do. Ask your prescriber: "With my current diabetes medicines, how much alcohol is safe, and should I check my glucose afterwards?"

Mounjaro can be injected with or without food, at any time of day, so meals do not change its effect. The label lists no specific supplement or herbal interactions. The Medication Guide still asks you to tell your healthcare provider about every vitamin and herbal supplement you take, since slower stomach emptying can affect anything swallowed.

Tell every surgeon, anesthesiologist and endoscopist that you take Mounjaro. The label reports rare aspiration during general anesthesia or deep sedation in people on GLP-1 drugs, even after normal fasting, and says data are too limited to set a holding rule.

Multi-society guidance led by the American Society of Anesthesiologists (October 2024) says most patients can continue GLP-1 drugs before elective surgery. Those at highest risk, such as people early in treatment, during dose escalation or with gut symptoms, may be told to stick to a liquid-only diet for 24 hours before the procedure.