Tirzepatide

What it is

Tirzepatide is a long-acting injected peptide that activates two gut-hormone receptors, the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor. It is given as a once-weekly injection under the skin.

What the research says

Large industry-funded trials show substantial weight loss in obesity, better blood sugar than semaglutide in type 2 diabetes, fewer breathing pauses in sleep apnoea, and fewer heart-failure events in obese patients with preserved ejection fraction. It was noninferior but not proven superior to dulaglutide for heart attack, stroke and cardiovascular death. Gastrointestinal side effects are common, gallbladder disease is more frequent, and most lost weight returns after stopping.

Evidence grade: Well established.

How it works

Drug class: Dual GIP and GLP-1 receptor agonist (incretin agonist), once-weekly injection

It mimics two gut hormones (GIP and GLP-1), which increases insulin release when blood sugar is high and reduces appetite, leading to weight loss. (Source 1)

Boxed warning

In rats, tirzepatide causes thyroid C-cell tumors.

(Source 2)

What it is used for

• In SURPASS-2, all doses lowered HbA1c more than semaglutide 1 mg (by 0.15 to 0.45 percentage points) over 40 weeks. Evidence: established. (Source 3)
• In SURMOUNT-1, weight fell 15.0% to 20.9% over 72 weeks versus 3.1% with placebo. Evidence: established. (Source 4)
• SURMOUNT-OSA reduced the apnoea-hypopnoea index by about 20 to 24 events per hour more than placebo at 52 weeks; approval status is from our understanding and should be confirmed against the label. Evidence: limited. (Source 5)
• Noninferior to dulaglutide for major cardiovascular events; superiority was not shown (HR 0.92, 95.3% CI 0.83 to 1.01). Evidence: limited. (Source 6)
• In SUMMIT, the composite of cardiovascular death or worsening heart failure fell from 15.3% to 9.9%; cardiovascular death alone was not reduced. We did not confirm current label status. Evidence: limited. (Source 7)

Interactions

• Oral hormonal contraceptives (label): Tirzepatide may reduce the reliability of the pill around the start and each dose increase; the label advises a non-oral or added barrier method for 4 weeks after each step. (Source 2)

Stopping it

• In a randomized withdrawal trial, people switched to placebo after 36 weeks regained much of the lost weight, while those who continued kept losing. (Source 8)

What goes wrong

Gallbladder or biliary disease was about twice as frequent with tirzepatide as with placebo or basal insulin. (Source 9)

• Meta-analysis, Low certainty.
• Size: 9 trials, 9,871 participants.
• Who: Adults with type 2 diabetes or obesity.
• How long: Trial durations.
• Result: RR 1.97 (95% CI 1.14 to 3.42) for the composite of gallbladder or biliary disease.
• Funding: Not stated in the abstract.

Limit of this finding: The paper reports this result with p = 0.558, but that p-value belongs to the test of heterogeneity (whether the trials disagreed with each other, I2 = 0%), not to the size of the effect. The evidence of an increased risk is the confidence interval (1.14 to 3.42), which lies above 1. The paper found no significant association with cholelithiasis, cholecystitis or biliary diseases taken separately.

the composite of gallbladder or biliary disease was significantly associated with tirzepatide compared with placebo or basal insulin (RR 1.97, [95% CI] 1.14 to 3.42

Gastrointestinal side effects are common: nausea in 17-22%, diarrhoea 13-16% and vomiting 6-10% of tirzepatide patients; serious adverse events 5-7% vs 3% with semaglutide. (Source 3)

• Randomized trial, Moderate certainty.
• Size: 1,879 patients.
• Who: Adults with type 2 diabetes.
• How long: 40 weeks.
• Result: Nausea 17-22% vs 18%; diarrhoea 13-16% vs 12%; vomiting 6-10% vs 8%; serious AEs 5-7% vs 3%.
• Funding: Industry-funded (Eli Lilly)

Serious adverse events were reported in 5 to 7% of the patients who received tirzepatide and in 3% of those who received semaglutide.

Adverse events led more people to stop tirzepatide than placebo. (Source 4)

• Randomized trial, High certainty.
• Size: 2,539 adults.
• Who: Adults with obesity.
• How long: 72 weeks.
• Result: Discontinuation for adverse events 4.3%, 7.1%, 6.2% vs 2.6% placebo.
• Funding: Industry-funded (Eli Lilly)

Adverse events caused treatment discontinuation in 4.3%, 7.1%, 6.2%, and 2.6% of participants receiving 5-mg, 10-mg, and 15-mg tirzepatide doses and placebo, respectively.

The label carries a boxed warning based on thyroid C-cell tumours in rats; human relevance is unknown. (Source 2)

• Official position, Certainty not rated.
• Size: Not applicable.
• Who: Label position (Revised 01/2026)
• How long: Not applicable.
• Result: Not applicable.
• Funding: Manufacturer label approved by FDA.

In rats, tirzepatide causes thyroid C-cell tumors.

What the evidence supports

In adults with obesity without diabetes, tirzepatide produced large weight loss versus placebo over 72 weeks. (Source 4)

• Randomized trial, High certainty.
• Size: 2,539 adults.
• Who: Adults with BMI 30+ or 27+ with a weight-related complication, no diabetes.
• How long: 72 weeks.
• Result: Mean weight change -15.0% (5 mg), -19.5% (10 mg), -20.9% (15 mg) vs -3.1% placebo; 5% or more loss in 85-91% vs 35%.
• Funding: Industry-funded (Eli Lilly)

The mean percentage change in weight at week 72 was -15.0% (95% confidence interval [CI], -15.9 to -14.2) with 5-mg weekly doses of tirzepatide

In type 2 diabetes, tirzepatide lowered HbA1c and weight more than semaglutide 1 mg. (Source 3)

• Randomized trial, Moderate certainty.
• Size: 1,879 patients.
• Who: Adults with type 2 diabetes on metformin.
• How long: 40 weeks (open-label)
• Result: HbA1c differences vs semaglutide -0.15 to -0.45 percentage points; weight differences -1.9 to -5.5 kg.
• Funding: Industry-funded (Eli Lilly)

Tirzepatide at all doses was noninferior and superior to semaglutide.

In obstructive sleep apnoea with obesity, tirzepatide reduced breathing events per hour versus placebo. (Source 5)

• Randomized trial, Moderate certainty.
• Size: Two trials (with and without PAP therapy)
• Who: Adults with moderate-to-severe OSA and obesity.
• How long: 52 weeks.
• Result: Treatment difference -20.0 (trial 1) and -23.8 (trial 2) events per hour.
• Funding: Industry-funded (Eli Lilly)

for an estimated treatment difference of -20.0 events per hour (95% CI, -25.8 to -14.2) (P<0.001)

In heart failure with preserved ejection fraction and obesity, tirzepatide lowered the composite of cardiovascular death or worsening heart failure. (Source 7)

• Randomized trial, Moderate certainty.
• Size: 731 patients.
• Who: Adults with HFpEF (EF 50%+) and BMI 30+.
• How long: Median 104 weeks follow-up.
• Result: 9.9% vs 15.3% (HR 0.62, 95% CI 0.41 to 0.95); absolute difference about 5.4 percentage points.
• Funding: Industry-funded (Eli Lilly)

Adjudicated death from cardiovascular causes or a worsening heart-failure event occurred in 36 patients (9.9%) in the tirzepatide group and in 56 patients (15.3%) in the placebo group

What the evidence does not support

In SUMMIT, cardiovascular death on its own was not reduced (few events). (Source 7)

• Randomized trial, Low certainty.
• Size: 731 patients.
• Who: Adults with HFpEF and obesity.
• How long: Median 104 weeks.
• Result: CV death 2.2% vs 1.4% (HR 1.58, 95% CI 0.52 to 4.83).
• Funding: Industry-funded (Eli Lilly)

adjudicated death from cardiovascular causes occurred in 8 patients (2.2%) and 5 patients (1.4%), respectively (hazard ratio, 1.58; 95% CI, 0.52 to 4.83)

Against dulaglutide in type 2 diabetes with cardiovascular disease, tirzepatide was noninferior but did not show superiority for major cardiovascular events. (Source 6)

• Randomized trial, High certainty.
• Size: 13,165 patients (modified ITT)
• Who: Adults with type 2 diabetes and atherosclerotic cardiovascular disease.
• How long: Event-driven trial.
• Result: 12.2% vs 13.1% (HR 0.92; 95.3% CI 0.83 to 1.01; P = 0.09 for superiority).
• Funding: Industry-funded (Eli Lilly)

A primary end-point event occurred in 801 patients (12.2%) in the tirzepatide group and 862 (13.1%) in the dulaglutide group (hazard ratio, 0.92; 95.3% confidence interval, 0.83 to 1.01; P = 0.003 for noninferiority; P = 0.09 for superiority).

A meta-analysis of trials did not find a significant increase in pancreatitis with tirzepatide. (Source 9)

• Meta-analysis, Low certainty.
• Size: 9 trials, 9,871 participants.
• Who: Adults with type 2 diabetes or obesity.
• How long: Trial durations.
• Result: RR 1.46 (95% CI 0.59 to 3.61) for pancreatitis.
• Funding: Not stated in the abstract.

Limit of this finding: The p = 0.436 in this quote belongs to the test of heterogeneity (whether the trials disagreed with each other, I2 = 0%), not to a test of whether tirzepatide changed pancreatitis risk. The evidence that there was no significant increase is the confidence interval (0.59 to 3.61), which includes 1. That interval is wide, so a real increase cannot be ruled out.

an increased risk of pancreatitis was not found to be significantly associated with tirzepatide (RR 1.46, [95% CI] 0.59 to 3.61; I2 = 0.0%, p = 0.436)

How much

• Reference intake: Dosing is set by the prescriber. As a position, the Zepbound label (01/2026) describes starting at 2.5 mg weekly and increasing in 2.5 mg steps at least 4 weeks apart. (Source 2)
• Upper limit: Label position (01/2026): maximum recommended dosage 15 mg once weekly. (Source 2)
• Studied: SURMOUNT-1: 5, 10 or 15 mg once weekly for 72 weeks, including 20 weeks of dose escalation. (Source 4)
• Studied: SURMOUNT-4: maximum tolerated 10 or 15 mg weekly during a 36-week lead-in, then continued or switched to placebo. (Source 8)

A common belief, and what the research shows

The belief: Once the weight is off, tirzepatide can be stopped without regain.

What the research shows: SURMOUNT-4: "Overall, 300 participants (89.5%) receiving tirzepatide at 88 weeks maintained at least 80% of the weight loss during the lead-in period compared with 16.6% receiving placebo (P < .001)."

Questions and answers

What is it?

A once-weekly injected medicine that activates the GIP and GLP-1 receptors, two gut-hormone receptors. (Source 1)

What does it do in the body?

It lowers blood sugar and causes substantial weight loss. In SURMOUNT-1, average weight fell by 15% to 21% over 72 weeks versus 3% with placebo. (Source 4)

Is it good or bad for you?

For obesity, type 2 diabetes, sleep apnoea and HFpEF with obesity, industry-funded trials show clear benefits. Harms include common gastrointestinal effects, more gallbladder disease, and a rodent thyroid tumour signal of unknown human relevance. (Source 9)

How do you get more of it?

Prescription only; the prescriber sets the dose. The label describes stepwise dose increases up to a maximum of 15 mg weekly, as a position. (Source 2)

If it is harmful, what reduces it?

Stopping is possible without a withdrawal syndrome being described in what we read, but weight tends to come back: in SURMOUNT-4, placebo patients regained 14% of body weight over 52 weeks. (Source 8)

Why might someone be low in it or missing it?

Does not apply: tirzepatide is a synthetic drug, not something the body makes or needs. (Source 1)

We searched: Trial abstracts and label read for this entry; question does not apply to a drug.

Which whole foods contain it or feed it?

Does not apply: no food contains tirzepatide. We found no documented food or supplement interaction in the sources read; the label interaction we found concerns oral contraceptives. (Source 2)

We searched: Zepbound label (01/2026) highlights; trial abstracts.

What happens if you do not have it?

Does not apply as a deficiency. Without it (placebo arms), weight loss in trials was small: 3.1% over 72 weeks in SURMOUNT-1. (Source 4)

How can you test for it?

No test is used to measure tirzepatide; response is followed through weight, HbA1c and other clinical measures in trials. (Source 3)

We searched: Label and trial abstracts read; no drug-level testing literature searched.

References

1. The New England Journal of Medicine. Tirzepatide for Heart Failure with Preserved Ejection Fraction and Obesity (SUMMIT) - background. 2025. PMID 39555826, DOI 10.1056/NEJMoa2410027. Read the source
2. US FDA / Eli Lilly. ZEPBOUND (tirzepatide) injection prescribing information (Revised 01/2026). 2026. Read the source
3. The New England Journal of Medicine. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2). 2021. PMID 34170647, DOI 10.1056/NEJMoa2107519. Read the source
4. The New England Journal of Medicine. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). 2022. PMID 35658024, DOI 10.1056/NEJMoa2206038. Read the source
5. The New England Journal of Medicine. Tirzepatide for the Treatment of Obstructive Sleep Apnea and Obesity (SURMOUNT-OSA). 2024. PMID 38912654, DOI 10.1056/NEJMoa2404881. Read the source
6. The New England Journal of Medicine. Cardiovascular Outcomes with Tirzepatide versus Dulaglutide in Type 2 Diabetes (SURPASS-CVOT). 2025. PMID 41406444, DOI 10.1056/NEJMoa2505928. Read the source
7. The New England Journal of Medicine. Tirzepatide for Heart Failure with Preserved Ejection Fraction and Obesity (SUMMIT) - results. 2025. PMID 39555826, DOI 10.1056/NEJMoa2410027. Read the source
8. JAMA. Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical Trial. 2024. PMID 38078870, DOI 10.1001/jama.2023.24945. Read the source
9. Frontiers in Endocrinology. Safety issues of tirzepatide (pancreatitis and gallbladder or biliary disease) in type 2 diabetes and obesity: a systematic review and meta-analysis. 2023. PMID 37908750, DOI 10.3389/fendo.2023.1214334. Read the source