Tirzepatide, two receptors, deeper response

What tirzepatide is

Tirzepatide is Eli Lilly's once-weekly injectable peptide. It is a dual agonist — a single molecule that activates both GLP-1 and GIP receptors. This dual-incretin design is the key thing distinguishing it from semaglutide and other GLP-1 monoagonists, and the reason it produces, in head-to-head comparisons, deeper weight loss and tighter glycaemic control.

Brand names:

• Mounjaro — approved globally (including India) for type 2 diabetes and, in many markets including India, for chronic weight management. For the Indian launch, pricing, and availability, see our Mounjaro guide.
• Zepbound — the obesity-specific brand used in the United States

In India, the same product — Mounjaro — covers both indications.

Why the dual mechanism matters

GLP-1 receptor agonism is well understood: appetite suppression, slowed gastric emptying, glucose-dependent insulin release. GIP receptor agonism adds two important effects:

• Improved insulin sensitivity in adipose tissue — particularly in visceral fat depots
• Increased energy expenditure — modest, but real

The mechanism's downstream effect is that tirzepatide produces, on average, larger and more consistent weight loss than semaglutide, with a somewhat better balance of fat loss to lean mass loss. In SURMOUNT-1, fat mass reduction was approximately three times greater than lean mass reduction.

The evidence

SURPASS-2 — the head-to-head with semaglutide

SURPASS-2 (Frías et al., NEJM, 2021) — The defining head-to-head. 1,879 adults with T2D, on metformin, randomised to tirzepatide (5, 10, or 15 mg) or semaglutide 1 mg, over 40 weeks. HbA1c reductions: 2.01% (5 mg), 2.24% (10 mg), 2.30% (15 mg) for tirzepatide vs 1.86% for semaglutide. Weight loss: 7.8, 10.3, and 12.4 kg respectively for tirzepatide vs 6.2 kg for semaglutide.

SURMOUNT-1 — the obesity registration trial

SURMOUNT-1 (Jastreboff et al., NEJM, 2022). 2,539 adults with obesity or overweight (without T2D), 72-week trial. Weight loss: 15.0% (5 mg), 19.5% (10 mg), and 20.9% (15 mg) vs 3.1% for placebo. About 9 in 10 participants on tirzepatide lost weight. A 3-year follow-up (Jastreboff et al., NEJM, 2024) showed that two-thirds of trial completers maintained their lowest weight or had regained no more than 5%, and progression from prediabetes to T2D was dramatically reduced.

SURMOUNT-2 — tirzepatide in T2D + obesity

SURMOUNT-2 (Garvey et al., Lancet, 2023). Tirzepatide in adults with T2D and obesity, 72 weeks. Mean weight loss of 14.7% at the 15 mg dose versus 3.2% on placebo — clinically meaningful since T2D patients typically lose less weight on GLP-1 therapy than non-diabetics.

SURMOUNT-OSA — sleep apnoea outcomes

SURMOUNT-OSA (Malhotra et al., NEJM, 2024). Two parallel trials in adults with moderate-to-severe obstructive sleep apnoea and obesity. Tirzepatide reduced the apnoea-hypopnea index substantially compared with placebo, in both PAP-using and PAP-naïve populations, with concurrent reductions in systolic blood pressure and inflammatory markers.

SUMMIT — heart failure with preserved ejection fraction

SUMMIT (Packer et al., NEJM, 2024). 731 patients with HFpEF and obesity. Tirzepatide reduced the composite primary endpoint of cardiovascular death or worsening heart failure by ~38%, with substantial improvements in exercise tolerance and quality of life. The first medication to demonstrate a hard clinical-outcome benefit in obesity-related HFpEF.

Dosing and titration

Tirzepatide is escalated more gradually than semaglutide because of stronger GI effects at higher doses:

2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg

Each step typically lasts 4 weeks. Many patients achieve their goals at 7.5 or 10 mg without progressing to the maximum dose.

Side effects vs semaglutide

The side-effect profile is broadly similar — predominantly GI (nausea, constipation or diarrhoea, occasional vomiting, reflux), front-loaded during titration, mostly mild-moderate. In SURMOUNT-1, discontinuation for adverse events was ~6–7% across doses. Tirzepatide may produce slightly higher rates of GI symptoms than semaglutide at the most effective doses, balanced against greater weight loss.

The same precautions apply: contraindicated with personal/family history of medullary thyroid carcinoma or MEN-2 (see our thyroid guide for what this means in practice); not for use in pregnancy; caution in patients with severe gastroparesis or recent acute pancreatitis.

Formats in India and cold chain

Eli Lilly launched Mounjaro in India in March 2025 in single-dose vials at 2.5 mg and 5 mg strengths. The Central Drugs Standard Control Organisation (CDSCO) approved the Mounjaro KwikPen in June 2025; KwikPens (multi-dose prefilled pens covering doses up to 15 mg) became available later in 2025. The full dose range is now accessible in India.

Tirzepatide is more cold-chain sensitive than semaglutide: it should be refrigerated at 2–8°C, and once removed from refrigeration can be stored at room temperature (below 30°C) for a limited window — check the specific product label, typically around 21 days. In an Indian summer or monsoon, this matters. Practical advice: keep the pen in the main refrigerator compartment (not the door, where temperatures swing); transport in an insulated bag with a gel pack; do not leave the pen in a vehicle or on a windowsill.

When tirzepatide makes more sense than semaglutide

• When weight loss is the primary goal and a deeper response is desired
• When HbA1c remains above target on adequate semaglutide doses
• For patients with HFpEF and obesity (SUMMIT is the only randomised trial showing event reduction in this specific phenotype)
• For moderate-to-severe obstructive sleep apnoea with obesity (SURMOUNT-OSA evidence)
• When the patient has prediabetes and high progression risk (SURMOUNT-1 3-year data are particularly striking)

When semaglutide may be preferred: longer real-world track record, broader Indian generic availability post-March 2026, and a substantial cardiovascular outcomes database in non-diabetic obesity (SELECT) and in CKD (FLOW) that tirzepatide does not yet match.

What to expect

Initial 2–4 weeks of mild GI symptoms, settling. Visible weight changes by week 4–6. Meaningful clinical change (HbA1c, blood pressure, weight) by week 12. Most patients reach the bulk of their response between months 6 and 18, depending on the dose they tolerate.

1. Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2). N Engl J Med. 2021;385(6):503–515.
2. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205–216.
3. Garvey WT, Frias JP, Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2). Lancet. 2023;402(10402):613–626.
4. Malhotra A, Grunstein RR, Fietze I, et al. Tirzepatide for the Treatment of Obstructive Sleep Apnea and Obesity (SURMOUNT-OSA). N Engl J Med. 2024;391(13):1193–1205.
5. Packer M, Zile MR, Kramer CM, et al. Tirzepatide for Heart Failure with Preserved Ejection Fraction and Obesity (SUMMIT). N Engl J Med. 2024;391:S1—S15.