Mounjaro Year-1 Outcomes: What Real Users Actually Experience

What the first year actually looks like in the trials

SURMOUNT-1 assigned 2,539 adults to weekly tirzepatide 5, 10 or 15 mg or placebo for 72 weeks, including a 20-week dose-escalation period. Participants had a BMI of 30 or higher, or 27 or higher with at least one weight-related complication, and no diabetes. Mean starting weight was 104.8 kg and mean BMI 38.0 [1].

At week 72 the mean weight change was -15.0% on 5 mg, -19.5% on 10 mg and -20.9% on 15 mg, against -3.1% on placebo [1]. Weight loss of at least 5% occurred in 85%, 89% and 91% of participants versus 35% on placebo, and loss of at least 20% occurred in 50% of the 10 mg group and 57% of the 15 mg group [1].

That is a 72-week result, not a 12-month one, which matters when you read a post that says 'one year in' [1]. Individual forum or review posts are not directly comparable with these controlled trial averages. SURMOUNT-4 went further, following participants to week 88 [5].

Mounjaro's label is for diabetes, not weight loss

The Mounjaro label covers two uses: as an adjunct to diet and exercise to improve glycemic control in adults and children 10 years and older with type 2 diabetes, and to reduce the risk of major cardiovascular events in adults with type 2 diabetes at high risk for them [3]. It is not labeled for weight loss [3].

Reviews that quantify pounds lost are borrowing from the weight-management trials of tirzepatide in people with obesity [1][2], not from the Mounjaro label's diabetes data. Zepbound is the tirzepatide brand approved for weight management and for moderate to severe obstructive sleep apnea in adults with obesity.

On the cardiovascular side, SURPASS-CVOT compared tirzepatide up to 15 mg with dulaglutide 1.5 mg in 13,165 adults with type 2 diabetes and atherosclerotic cardiovascular disease. The composite of cardiovascular death, heart attack or stroke occurred in 12.2% versus 13.1% (hazard ratio 0.92, 95.3% CI 0.83 to 1.01), meeting noninferiority but not superiority [6].

How much do people with type 2 diabetes lose?

SURMOUNT-2 enrolled 938 adults with a BMI of 27 or higher and HbA1c of 7% to 10%, and compared 10 mg and 15 mg with placebo over 72 weeks. Weight fell 12.8% on 10 mg and 14.7% on 15 mg versus 3.2% on placebo, and at least 5% weight loss occurred in 79.2% and 82.8% versus 32.5% [2]. Those average losses were smaller than the ones reported in SURMOUNT-1, which excluded diabetes [1][2].

SURPASS-2 is shorter and reports kilograms. In 1,879 adults with type 2 diabetes on metformin, 40 weeks of tirzepatide 5, 10 or 15 mg produced weight changes of -7.6 kg, -9.3 kg and -11.2 kg, versus -5.7 kg with semaglutide 1 mg. HbA1c fell 2.01, 2.24 and 2.30 percentage points versus 1.86 [4].

Common side effects in Mounjaro's diabetes trials

In Mounjaro's own pooled placebo-controlled trials (SURPASS-1 and SURPASS-5: 235 on placebo, 237 on 5 mg, 240 on 10 mg, 241 on 15 mg, mean exposure 36.6 weeks), reactions reported in at least 5% of Mounjaro-treated patients were nausea, diarrhea, decreased appetite, vomiting, constipation, dyspepsia and abdominal pain. The rates (placebo, 5 mg, 10 mg, 15 mg) were [3]:

• Nausea: 4%, 12%, 15%, 18%
• Diarrhea: 9%, 12%, 13%, 17%
• Decreased appetite: 1%, 5%, 10%, 11%
• Vomiting: 2%, 5%, 5%, 9%
• Constipation: 1%, 6%, 6%, 7%
• Dyspepsia: 3%, 8%, 8%, 5%
• Abdominal pain: 4%, 6%, 5%, 5%

The label says most reports of nausea, vomiting or diarrhea occurred during dose escalation and decreased over time [3]. Discontinuation for a gastrointestinal reaction in that pool was 3.0%, 5.4% and 6.6% versus 0.4% on placebo, and acute gallbladder disease was reported by 0.6% of Mounjaro-treated patients and 0% on placebo [3]. The label also states that adverse reaction rates from different trials cannot be directly compared, because the trials are run under widely varying conditions [3].

Hair loss does not appear among the adverse reactions in the Mounjaro label [3].

Does the weight come back if treatment stops?

SURMOUNT-4 answers this most directly. Of 783 people who entered a 36-week open-label tirzepatide lead-in, 670 were randomized after losing an average of 20.9% of their body weight; they then continued tirzepatide or switched to placebo for 52 more weeks [5]. From week 36 to week 88, weight changed by -5.5% in those who continued and +14.0% in those switched to placebo, a 19.4 percentage-point difference [5].

Tirzepatide versus semaglutide in the same year

SURMOUNT-5 was an open-label head-to-head trial in 751 adults with obesity and no type 2 diabetes, comparing maximum tolerated tirzepatide (10 or 15 mg) with maximum tolerated semaglutide (1.7 or 2.4 mg) over 72 weeks. Weight change was -20.2% versus -13.7%, and waist circumference fell 18.4 cm versus 13.0 cm, both significant [7].

What happens to lean mass

A body-composition substudy of SURMOUNT-1 measured 160 participants with DXA scans at baseline and week 72: 124 pooled tirzepatide and 36 placebo, 73% female, mean weight 102.5 kg [8]. Weight changed -21.3%, fat mass -33.9% and lean mass -10.9% with tirzepatide, versus -5.3%, -8.2% and -2.6% with placebo [8]. About 75% of the weight lost was fat mass and about 25% lean mass, the same proportion seen on placebo [8]. DXA cannot separate muscle from other lean tissue.

What the label tells you to watch for

The boxed warning covers thyroid C-cell tumors: tirzepatide caused dose- and duration-dependent thyroid C-cell tumors in rats at clinically relevant exposures, and whether this applies to humans, including medullary thyroid carcinoma, is unknown [3]. Mounjaro is contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2, and in anyone with a known serious hypersensitivity to tirzepatide or an excipient [3].

The label says to discontinue Mounjaro if pancreatitis is suspected, and to monitor kidney function in patients whose gastrointestinal reactions could lead to volume depletion [3]. Mounjaro can raise the risk of low blood sugar when used with insulin or a sulfonylurea, and the label says a reduction in the dose of those medicines may be needed [3]. Pulmonary aspiration has been reported during general anesthesia or deep sedation in patients receiving GLP-1 receptor agonists, and the label says patients should tell their healthcare providers about planned surgeries or procedures [3]. Mounjaro is not recommended in severe gastroparesis [3]. For oral hormonal contraceptives, the label advises switching to a non-oral method or adding a barrier method for 4 weeks after starting and for 4 weeks after each dose escalation [3].

How the dose is built up

The label gives a Mounjaro starting dose of 2.5 mg once weekly, increased in 2.5 mg steps after at least 4 weeks on the current dose if more glycemic control is needed, to a maximum of 15 mg weekly in adults and 10 mg weekly in pediatric patients 10 years and older [3]. It says to inject into the abdomen, thigh or back of the upper arm (the upper arm by another person), rotating sites, at any time of day with or without meals [3]. For a missed dose, the label says to give it as soon as possible within 4 days (96 hours); after that, skip it and resume the regular schedule [3].