Dr. Pep

Peptides · GIP/GLP-1 dual receptor agonist

Tirzepatide: what the studies show

Every line below comes from a study, label or regulator record, checked by two models, with the source linked. Information, not medical advice. For adults 18+.

What it is

  • Tirzepatide is a once-weekly injection that activates both the GIP and GLP-1 receptors. It is sold as Mounjaro (type 2 diabetes) and Zepbound (weight and sleep apnoea).[1][2]
  • The Mounjaro label (2026) lists blood-sugar control in adults and children 10 and older with type 2 diabetes, and fewer major heart events in adults with type 2 diabetes at high heart risk.[1]
  • The Zepbound label (2026) lists weight reduction and long-term maintenance in adults with obesity, or overweight with a related condition, plus moderate to severe obstructive sleep apnoea in adults with obesity. It is used with diet and exercise.[2]

Bottom line

  • Tirzepatide is an approved prescription drug with large randomised trials showing about 15-21% weight loss at 72 weeks, but the weight comes back if it is stopped and stomach side effects are common. Unbranded 'research' vials are unapproved products.[3][4][2][5]

What the human studies found

  • SURMOUNT-1 (double-blind RCT, 2,539 adults with obesity, no diabetes, 72 weeks): weight fell 15.0%, 19.5% and 20.9% on tirzepatide 5, 10 and 15 mg weekly, versus 3.1% on placebo. 50% (10 mg) and 57% (15 mg) lost 20% or more, versus 3% on placebo.[3]
  • SURMOUNT-2 (RCT, 938 adults with obesity and type 2 diabetes, 72 weeks): weight fell 12.8% on 10 mg and 14.7% on 15 mg, versus 3.2% on placebo.[6]
  • SURMOUNT-3 (RCT, 579 adults who had already lost 5% or more through a 12-week lifestyle programme): a further 18.4% loss on tirzepatide versus a 2.5% gain on placebo over 72 weeks.[7]
  • SURMOUNT-4 (RCT, 670 adults after a 36-week lead-in with a mean 20.9% loss): continuing tirzepatide gave a further 5.5% loss, while switching to placebo gave a 14.0% regain. 89.5% of those who continued kept at least 80% of the lead-in loss, versus 16.6% on placebo.[4]
  • SURMOUNT-OSA (two RCTs in adults with moderate to severe sleep apnoea and obesity, 52 weeks): the apnoea-hypopnoea index fell by 25.3 and 29.3 events an hour on tirzepatide, versus 5.3 and 5.5 on placebo.[8]
  • SURPASS-2 (RCT, 1,879 adults with type 2 diabetes, tirzepatide 5, 10 or 15 mg versus semaglutide 1 mg): HbA1c fell 2.01 to 2.30 points on tirzepatide versus 1.86 on semaglutide, and weight loss was larger by 1.9, 3.6 and 5.5 kg.[9]

Known risks and side effects

  • Boxed warning (Zepbound): risk of thyroid C-cell tumours, based on rat studies. Not for people with a personal or family history of medullary thyroid cancer or MEN 2.[2]
  • Zepbound label trials: nausea 25-29% versus 8% on placebo, diarrhoea 19-23% versus 8%, vomiting 8-13% versus 2%. Across the weight-loss trials, 4.8%, 6.3% and 6.7% on 5, 10 and 15 mg stopped because of side effects.[2]
  • Other label warnings: severe stomach and bowel reactions (not recommended in severe gastroparesis), kidney injury from fluid loss, gallbladder disease, pancreatitis, serious allergic reactions, low blood sugar with insulin or sulfonylureas, and worsening diabetic retinopathy.[2]
  • In the SURPASS-2 trial of 1,879 adults with type 2 diabetes, nausea affected 17-22% on tirzepatide and 18% on semaglutide; vomiting 6-10% versus 8%.[9]

Legal status

  • FDA approved: Mounjaro and Zepbound (labels dated 2026).[1][2]
  • On 2024-12-19 FDA declared the tirzepatide injection shortage resolved, replacing its 2024-10-02 decision. FDA's page dated 2026-04-01 reminds compounders that section 503A and 503B conditions must be met.[10][11]
  • FDA announced (current as of 2026-04-30) that it proposes to exclude tirzepatide, semaglutide and liraglutide from the 503B bulks list, finding no clinical need for outsourcing facilities to compound them from bulk substance.[12]

Sources

  1. [1] Mounjaro (Tirzepatide) Injection, Solution Mounjaro Kwikpen (Tirzepatide) Injection, Solution prescribing information
  2. [2] Zepbound (Tirzepatide) Injection, Solution Zepbound (Tirzepatide) Injection, Solution Zepbound Kwikpen (Tirzepatide) Injection, Solution prescribing information
  3. [3] Tirzepatide Once Weekly for the Treatment of Obesity.
  4. [4] Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical Trial.
  5. [5] FDA: FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss (updated 2026)
  6. [6] Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2): a double-blind, randomised, multicentre, placebo-controlled, phase 3 trial.
  7. [7] Tirzepatide after intensive lifestyle intervention in adults with overweight or obesity: the SURMOUNT-3 phase 3 trial.
  8. [8] Tirzepatide for the Treatment of Obstructive Sleep Apnea and Obesity.
  9. [9] Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes.
  10. [10] FDA: Declaratory Order, Resolution of Shortages of Tirzepatide Injection Products (2024-12-19)
  11. [11] FDA: FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize (shortage resolution, end of enforcement discretion)
  12. [12] FDA: FDA Proposes to Exclude Semaglutide, Tirzepatide, and Liraglutide on 503B Bulks List (press announcement)