Mounjaro® and low blood sugar

How the labels count an episode

The US tables use two levels: a measured blood glucose below 54 mg/dL, and severe hypoglycemia, an episode in which another person had to give carbohydrate, glucagon or other emergency treatment ^[1]. Canada adds a third, milder level: symptoms together with a reading of 3.9 mmol/L (70 mg/dL) or lower ^[4]. MedlinePlus explains that blood sugar below 70 mg/dL is considered low, and that more severe symptoms such as unclear thinking or seizures tend to appear below 54 mg/dL ^[6].

The adult figures come from two 40-week placebo-controlled trials, shown separately: SURPASS-1, where Mounjaro® was the only diabetes medicine, and SURPASS-5, where it was added to basal insulin with or without metformin. The counts include four weeks of follow-up after treatment stopped and exclude episodes after a new glucose-lowering medicine was started ^[1].

Adults: on its own and with basal insulin

Each figure is the share of people with at least one episode in that category. The symptomatic rows come from the Canadian monograph ^[4].

With a sulfonylurea and other tablets

The US label says hypoglycemia was more frequent when Mounjaro® was combined with a sulfonylurea. In an adult trial of up to 104 weeks, readings below 54 mg/dL occurred in 13.8% on 5 mg, 9.9% on 10 mg and 12.8% on 15 mg, and severe episodes in 0.5%, 0% and 0.6% ^[1]. Canada identifies that trial as SURPASS-4 and adds its comparator: on insulin glargine, 21.6% had a low reading or severe episode and 1.1% a severe one ^[4].

With metformin in SURPASS-2, low readings or severe episodes occurred in 0.9%, 0.2% and 1.7% on the three tirzepatide doses against 0.4% on semaglutide 1 mg; with an SGLT2 inhibitor in SURPASS-3, in 1.8% to 2.7% against 8.6% on insulin degludec, with no severe episodes ^[4]. The European information summarises the pattern: low readings or severe episodes in 10% to 14% when tirzepatide was added to a sulfonylurea and 14% to 19% when added to basal insulin, with much lower rates otherwise ^[3].

Children aged 10 and older

In the 30-week pediatric trial no severe episodes were reported, and the US label names low blood sugar as one of three reactions more common in children than in adults ^[1]. Groups were small: in the insulin subgroup there were only 10 or 11 children per arm. The European information adds event rates: with basal insulin, 28.6% on tirzepatide against 10.0% on placebo; with metformin alone, 9.1% against 4.2% ^[3].

Why tirzepatide alone rarely causes lows

What the label supports: tirzepatide increases insulin release and lowers glucagon in a glucose-dependent manner, meaning the effect weakens as blood sugar falls ^[1]. That fits the monotherapy result above. The warning in section 5.3 is accordingly framed around combinations with insulin or insulin secretagogues such as sulfonylureas ^[1].

What reviews add: a meta-analysis of seven tirzepatide trials in type 2 diabetes found the incidence of hypoglycemia similar to placebo and lower than with basal insulin ^[5]. The NIH names insulin and sulfonylureas, which raise insulin levels for several hours, as the diabetes medicines that can cause lows ^[7].

In the EU, where Mounjaro® is also used for weight management, low blood sugar is listed as a side effect only for people with type 2 diabetes ^[3]. MedlinePlus notes that in people without diabetes, low blood sugar has other causes, such as alcohol, some non-diabetes medicines and serious illness ^[6].

What raises the risk

• Insulin or a sulfonylurea alongside Mounjaro®. The US label asks prescribers to consider lowering their doses when Mounjaro® starts; the European information recommends a stepwise reduction of insulin, guided by blood glucose self-monitoring ^[1][3].
• Eating much less. Tirzepatide lowers food intake, and the NIH lists skipped or delayed meals, too few carbohydrates and fasting as triggers in people on these medicines ^[1][7].
• Being sick, especially with vomiting, more physical activity than usual, and alcohol without enough food ^[7].
• Age 65 and over, earlier episodes of low blood sugar, or kidney disease, heart disease or problems with memory and thinking ^[7].
• Taking too much: the European leaflet notes that an overdose can cause low blood sugar and nausea or vomiting ^[3].

Signs, and what to do

The Medication Guide’s list runs from shakiness, sweating, hunger and a fast heartbeat to headache, blurred vision, slurred speech, confusion or drowsiness, dizziness, weakness, irritability or mood change and feeling jittery ^[2]. The NIH adds that lows during sleep can show as nightmares or crying out, sweat-damp sheets and feeling tired or confused on waking, and that very low levels can cause fainting or seizures ^[7].

MedlinePlus says people with diabetes should be taught by their provider how to treat a low, which may involve juice or another sugary drink, food, glucose tablets or glucagon ^[6]. The NIH suggests asking your doctor for a glucagon kit and teaching family or friends how to use it, and wearing a medical ID ^[7]. The European and Canadian information advise avoiding driving or using machines if you have signs of low blood sugar while on insulin or a sulfonylurea ^[3][4].

Questions for your diabetes team

Worth asking before or soon after starting: whether your insulin or sulfonylurea dose should change, how often to check your glucose, what reading counts as low for you, how to treat a low, what to do on sick days or when you can hardly eat, and whether a glucagon kit makes sense. Bring meter readings with times and what you ate. Any change to your medicines is your prescriber’s decision.

Mounjaro® is a registered trademark of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Eli Lilly and Company.

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