Tirzepatide

Definition

Tirzepatide is a 39-amino-acid synthetic peptide that activates both the GIP and GLP-1 receptors, the first dual incretin agonist approved in the United States; it is marketed for type 2 diabetes and for chronic weight management.

Engaging two incretin receptors rather than one produces larger average weight reductions than GLP-1 agonism alone, at the cost of a similar gastrointestinal tolerability profile.

Evidence

In SURMOUNT-1, 2,539 adults with obesity received weekly tirzepatide or placebo for 72 weeks; mean weight change was −15.0 percent at 5 mg, −19.5 percent at 10 mg, and −20.9 percent at 15 mg, against −3.1 percent with placebo ^[1].

As with semaglutide, the open questions are durability and long-term safety in broad use; efficacy against placebo is settled.

SURMOUNT-OSA enrolled 469 adults with obesity and moderate-to-severe obstructive sleep apnea in two trials separated by baseline PAP use. Tirzepatide reduced breathing-event frequency more than placebo over 52 weeks; the later weight-association analysis used the same study program, not a new independent trial ^{[9, 10]}. The sleep-apnea evidence review distinguishes fewer breathing events from a universal cure or permission to stop PAP.

Side effects

The Zepbound label lists the adverse reactions reported in at least 5 percent of treated patients: nausea, diarrhea, vomiting, constipation, abdominal pain, indigestion, injection site reactions, fatigue, hypersensitivity reactions, belching, hair loss and gastroesophageal reflux ^[3]. Gastrointestinal reactions are sometimes severe, and the label does not recommend the drug for people with severe gastroparesis ^[3].

A boxed warning covers thyroid C-cell tumors: tirzepatide caused them in rats, whether it does so in humans is unknown, and the drug is contraindicated for anyone with a personal or family history of medullary thyroid carcinoma or with multiple endocrine neoplasia syndrome type 2 ^[3].

The label's other warnings cover acute kidney injury from dehydration, acute gallbladder disease, acute pancreatitis, serious allergic reactions including anaphylaxis and angioedema, hypoglycemia when combined with insulin or an insulin secretagogue, diabetic retinopathy complications in patients with type 2 diabetes, and pulmonary aspiration during general anesthesia or deep sedation ^[3].

Compounded tirzepatide is not covered by that label. The FDA reports dosing errors with compounded GLP-1 injections and has received an adverse event report tied to a product labeled as compounded tirzepatide from a pharmacy that had not made it ^[4].

Educational summary of the cited sources, not medical advice; a prescriber weighs these risks against a person’s own history.

Lawful access

The approved products are the lawful supply route. The FDA declared the tirzepatide shortage resolved in October 2024, ending shortage-based compounding; the April 2026 proposal to exclude it from the 503B bulks list closes the outsourcing route, and patient-specific 503A compounding requires documented clinical need ^[2].

Telehealth programs in the supply panel provide prescriber-led GLP-1 treatment; molecule and formulation vary by provider and should be confirmed on the provider's own site.

Related molecules

The class comparison with semaglutide is drawn on the GLP-1 receptor agonists page; the approved status page lists the index's approved molecules.

Lilly's next incretin drugs sit on either side of this one. Orforglipron was approved on April 1, 2026 as Foundayo, for weight reduction in adults with obesity or with overweight and a weight-related condition ^[6]; it is a once-daily tablet and a small molecule rather than a peptide, with a molecular weight of 902 g/mol for its calcium salt against 4,813.53 Da for tirzepatide ^[5][3]. Retatrutide adds the glucagon receptor to tirzepatide's two and remains investigational; TRIUMPH-5, a phase 3 trial comparing the two directly, is registered with an estimated primary completion in November 2026 ^[7]. Novo Nordisk's CagriSema did not show non-inferiority to tirzepatide on weight loss in REDEFINE 4 ^[8]. The incretin pipeline tracker compares all of them.

Elsewhere in this index