Mounjaro and Hypoglycemia: When to Call the Doctor

Does Mounjaro cause low blood sugar on its own?

Tirzepatide is approved as Mounjaro to improve glycemic control in type 2 diabetes in adults and children 10 years and older, and to reduce cardiovascular risk in adults with type 2 diabetes at high risk [1]. The label builds its hypoglycemia warning around other glucose-lowering drugs: patients receiving Mounjaro with an insulin secretagogue such as a sulfonylurea, or with insulin, may have an increased risk of hypoglycemia, including severe hypoglycemia, and the risk may be lowered by reducing the dose of the sulfonylurea or insulin [1].

In the label's monotherapy trial (SURPASS-1), glucose under 54 mg/dL occurred in 0% of patients on each Mounjaro dose and 1% on placebo [1].

Who the risk actually falls on

• People on insulin. The label names insulin directly as a driver of hypoglycemia risk with Mounjaro [1].
• People on a sulfonylurea or meglitinide. NIDDK lists these as the two types of diabetes pills that can cause low blood glucose, with sulfonylureas raising insulin over several hours [2]. A review notes that sulfonylureas, especially the older ones, are linked to a greater prevalence of hypoglycemia [3].
• People aged 65 or older. NIDDK lists age 65 and above among the factors that make low blood glucose more likely [2].
• People with kidney disease, heart disease or cognitive impairment. NIDDK lists these conditions as risk factors, along with having had a low before [2].

What the label asks of prescribers

Section 7.1 of the Mounjaro label says that when Mounjaro is initiated, the prescriber should consider reducing the dose of a concomitantly used insulin secretagogue (for example a sulfonylurea) or insulin to reduce the risk of hypoglycemia [1]. Section 5.3 adds that patients on these medications should be told about the risk and taught the signs and symptoms of hypoglycemia [1]. Neither section states an amount for the reduction [1].

What the trial numbers show

In SURPASS-5, a 40-week trial of Mounjaro added to basal insulin with or without metformin, glucose under 54 mg/dL occurred in 16%, 19% and 14% of patients on 5 mg, 10 mg and 15 mg, versus 13% on placebo [1]. Severe hypoglycemia was reported in none of the placebo or 5 mg patients, 2% on 10 mg and 1% on 15 mg [1]. The label also states that hypoglycemia was more frequent when Mounjaro was used with a sulfonylurea [1].

The Zepbound label, a different tirzepatide product, gives a sulfonylurea comparison from SURMOUNT-2, a trial in adults with type 2 diabetes and obesity or overweight: glucose under 54 mg/dL in 10.3% of patients on a sulfonylurea versus 2.1% of those not on one. That figure comes from a Zepbound trial population, not a Mounjaro one.

What a low looks like

NIDDK describes a low as a blood glucose reading below 70 mg/dL for many people with diabetes, while noting that the number can differ from person to person [2].

Mild to moderate symptoms include feeling shaky or jittery, hungry, tired, dizzy or lightheaded, confused or irritable, a heartbeat that is too fast or not steady, a headache, and trouble seeing or speaking clearly [2]. When blood glucose gets very low, the brain stops working as it should: the person may lose consciousness or have a seizure [2]. NIDDK defines severely low blood glucose as a level that drops so low you cannot treat it yourself, and says severe hypoglycemia is dangerous and needs treatment right away [2]. Untreated, severe lows can cause passing out, coma or death [2].

Lows during sleep

NIDDK notes that blood glucose can fall while you sleep and stay low for hours [2]. Signs include crying out or having nightmares, sweating enough to make pajamas or sheets damp, and waking up tired, irritable or confused [2]. You may not wake up or notice anything at all [2].

Why slow stomach emptying matters

Tirzepatide slows gastric emptying. A review of GLP-1-based therapies describes that slowing as useful for lowering post-meal glucose but also as a source of hypoglycemia risk in people on insulin or sulfonylurea therapy [4].

When a low needs action

• Severe low (cannot treat it yourself, seizure, or loss of consciousness): NIDDK calls glucagon the best way to treat severely low blood glucose, and says family, friends and coworkers should call 911 right away after giving glucagon or if no glucagon kit is with the person [2].
• Mild-to-moderate low: NIDDK's steps are to eat or drink 15 to 20 grams of glucose or carbohydrate right away, check blood glucose again after 15 minutes, and repeat until the level is back in the target range [2].
• Repeated lows or lows you do not feel: NIDDK says repeated low episodes can lead to hypoglycemia unawareness, where no symptoms are noticed until glucose has dropped very low [2]. With Mounjaro plus insulin or a sulfonylurea, the label's lever is the dose of that other medicine, and its dose-reduction advice is addressed to prescribers [1].