GIP/GLP-1 Dual Agonists: How to Select the Right Agent Within the Class

How many GIP/GLP-1 dual agonists are approved?

One. Tirzepatide's labeling describes it as a GIP receptor and GLP-1 receptor agonist, a dual agonist rather than a pure GLP-1 agonist, even though it is usually grouped with the GLP-1 drugs [2]. It comes in two brands with different labeled uses: Mounjaro for type 2 diabetes [1] and Zepbound for weight reduction and sleep apnea [2].

Other weight-loss peptides sometimes mentioned alongside it are not approved medicines. No FDA-approved retatrutide or cagrilintide product exists, and FDA says neither can be used in compounding under federal law and neither has been found safe and effective for any condition [6]. Compounded tirzepatide is likewise not FDA approved and is not reviewed for safety, effectiveness or quality [6].

That leaves a narrow decision: which tirzepatide label fits, and when a selective GLP-1 agonist is the better match.

Mounjaro or Zepbound: two labels, different uses

Mounjaro is labeled for type 2 diabetes; Zepbound is labeled for weight reduction and sleep apnea [1][2]. Both are given as a once-weekly subcutaneous injection [2][1]. Both carry a boxed warning about thyroid C-cell tumors seen in rodents, with human relevance unknown, and both are contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN 2 [1][2]. Zepbound's label also says use with another GLP-1 receptor agonist is not recommended [2].

The practical fork is the indication: treatment of type 2 diabetes sits under the Mounjaro label [1], while weight reduction or sleep apnea sits under Zepbound [2].

Head-to-head on weight: SURMOUNT-5

In SURMOUNT-5, 751 adults with obesity and no diabetes were assigned to maximum tolerated weekly doses of tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) for 72 weeks in an open-label design [3]. Weight fell 20.2% with tirzepatide and 13.7% with semaglutide, and waist circumference fell 18.4 cm versus 13.0 cm; participants on tirzepatide were more likely to reach weight reductions of at least 10%, 15%, 20% and 25% [3].

The placebo-controlled trials of each drug used different populations and designs and are not directly comparable. In SURMOUNT-1, 2,539 adults without diabetes lost 15.0%, 19.5% and 20.9% at 5, 10 and 15 mg versus 3.1% on placebo at 72 weeks [7]. In STEP 1, 1,961 adults lost 14.9% on semaglutide 2.4 mg versus 2.4% on placebo at 68 weeks [8]. The head-to-head trial is the cleaner comparison.

Head-to-head on glucose: SURPASS-2

In 1,879 adults with type 2 diabetes over 40 weeks in an open-label design, tirzepatide 5, 10 and 15 mg lowered HbA1c by 2.01, 2.24 and 2.30 points, against 1.86 points for semaglutide 1 mg; weight reductions were 1.9, 3.6 and 5.5 kg greater than with semaglutide [4].

Why the dual agonist pulls ahead is not settled. The tirzepatide label says nonclinical studies suggest the added GIP activity may further contribute to regulation of food intake, but neither head-to-head trial establishes that the GIP component explains the difference [2][4][3].

Cardiovascular outcomes

The large cardiovascular outcome results cited here are semaglutide results. In SELECT, 17,604 adults with established cardiovascular disease and a BMI of 27 or higher but no diabetes received semaglutide 2.4 mg or placebo; mean follow-up was 39.8 months [9]. Cardiovascular death, heart attack or stroke occurred in 6.5% versus 8.0% (hazard ratio 0.80) [9]. In SUSTAIN-6, 3,297 adults with type 2 diabetes over 104 weeks had those events at 6.6% versus 8.9% (hazard ratio 0.74) [10]. Both are semaglutide trials, so this evidence applies to semaglutide rather than to tirzepatide.

What each label says to watch for

Gastrointestinal effects dominate and are worst during dose escalation. In the Zepbound weight-management trials at 15 mg, nausea occurred in 28%, vomiting 13%, diarrhea 23% and constipation 11%, against 8%, 2%, 8% and 5% on placebo; 6.7% stopped for adverse reactions versus 3.4% on placebo, and hair loss was reported by 4% to 5% versus 1% [2]. The Wegovy label reports nausea 44%, vomiting 24%, diarrhea 30% and constipation 24% versus 16%, 6%, 16% and 11%, with 6.8% versus 3.2% stopping and hair loss 3% versus 1% [5]. The labels caution that rates from different trials cannot be directly compared [5].

The Wegovy and Foundayo labels list acute pancreatitis, severe gastrointestinal reactions with the drug not recommended in severe gastroparesis, acute kidney injury from dehydration, gallbladder disease, hypoglycemia when combined with insulin or a sulfonylurea, serious hypersensitivity, diabetic retinopathy complications in type 2 diabetes, and pulmonary aspiration during general anesthesia or deep sedation [5][11]. The Zepbound label reports mean resting heart rate increases of 1 to 3 beats per minute [2].

The interaction that differs by product

The tirzepatide label advises switching to a non-oral contraceptive or adding a barrier method for 4 weeks after starting and for 4 weeks after each dose increase [2]. Semaglutide labels carry no such advice, and a tablet interaction study found no clinically significant change in ethinyl estradiol or levonorgestrel [5]. The Wegovy and Foundayo labels warn that hypoglycemia risk rises when the drug is combined with insulin or a sulfonylurea and advise considering a lower dose of those medicines when starting [5][11].

What happens when treatment stops

The randomized withdrawal data cited here come from semaglutide. In STEP 4, 803 adults who reached semaglutide 2.4 mg during a 20-week run-in were then assigned to continue it or switch to placebo for 48 weeks; weight changed by another -7.9% on continued treatment and +6.9% on placebo, a 14.8-point difference [12].