Tirzepatide

One weekly molecule that hits two gut-hormone receptors, and the strongest weight-loss results of any approved drug.

Evidence: AApproved what's this?
Grade A. Large randomised trials, approved by FDA, EMA and CDSCO.
Also known as: Mounjaro (type 2 diabetes) · Zepbound (weight, sleep apnoea) · LY3298176
Class: Dual GIP + GLP-1 receptor agonist, the first "twincretin". Approved prescription medicine.

The 30-second version

WhatA 39-amino-acid peptide with a fatty-acid tail, so a single dose lasts about a week.

ResultsAround 15–21% average weight loss at 72 weeks in SURMOUNT-1. It beat semaglutide head to head.

The honest catchWeight tends to come back after stopping, and some of what is lost can be muscle without protein and training.

What it is

Your gut releases two "incretin" hormones after a meal, GLP-1 and GIP. Both tell the pancreas to release insulin and the brain that food has arrived. Semaglutide copies GLP-1 only. Tirzepatide was engineered to activate both receptors from a single molecule. That second receptor is the main reason it outperforms GLP-1-only drugs.

A fatty-acid side chain lets it bind albumin in the blood, which stretches its half-life to about five days and makes once-weekly injection possible. Eli Lilly sells it as Mounjaro for type 2 diabetes and Zepbound for chronic weight management and obstructive sleep apnoea. Mounjaro has been available in India since 2025.

How it works

Weekly dose under the skin. The albumin-bound drug releases slowly over about five days.

GLP-1 receptor. Quiets hunger signals in the brain and slows stomach emptying, so you feel full sooner and for longer.

GIP receptor. Adds insulin release, changes how fat tissue handles energy, and may ease nausea from GLP-1 activity.

Glucose-dependent. Insulin is boosted mainly when blood sugar is high, which keeps the risk of lows low.

Outcome. People eat less, glucose and lipids improve, and weight falls steadily over months.

What the research shows

SURMOUNT-1 (2,539 adults with obesity, 72 weeks): average weight loss was 15.0% at 5 mg, 19.5% at 10 mg and 20.9% at 15 mg, against 3.1% on placebo¹. More than half of people on the higher doses lost at least a fifth of their body weight.

SURMOUNT-5 was the first head-to-head trial against semaglutide. Tirzepatide produced 20.2% weight loss versus 13.7% at 72 weeks².

Three-year follow-up. In people with prediabetes, the SURMOUNT-1 extension to 176 weeks showed weight loss was maintained while treatment continued, and progression to type 2 diabetes fell by about 94% versus placebo³.

The SURPASS trials established better glucose control than comparator diabetes drugs, and SURMOUNT-OSA led to approval for obstructive sleep apnoea in adults with obesity⁴.

Whether tirzepatide works is settled. The open questions are how to keep the muscle and how to keep the weight off.

Evidence at a glance

Use	Grade	Best evidence	Main gap	Read
Weight loss	AApproved	Up to ~21% at 72 weeks¹	Regain after stopping	Best approved option
vs semaglutide	AApproved	20.2% vs 13.7%, head to head²	—	Superior
Diabetes prevention	AApproved	~94% less progression over 3 years³	Prediabetes group only	Striking
Type 2 diabetes, OSA	AApproved	Approved indications⁴	—	Established

Dosing: the approved schedule

Prescription medicine. The schedule below comes from the official prescribing information and is shown so you can understand it. Starting, adjusting or stopping should happen with a doctor, especially if you take insulin or other diabetes drugs.

Step	Weekly dose	Minimum time	What it's for
1	2.5 mg	4 weeks	Starter dose for tolerance only, not meant to cause weight loss
2	5 mg	4 weeks +	First maintenance option; appetite effect becomes clear
3	7.5 mg	4 weeks +	A new wave of GI effects is common; many people stay here
4	10 mg	4 weeks +	Maintenance option
5	12.5 mg	4 weeks +	Watch for under-eating and muscle loss
6	15 mg	Maintenance	Maximum dose. Not everyone needs it.

Move up only after at least four weeks on a dose, once side effects have settled. Stay put if results are good. The lowest dose that works is the right one. Step back to the last dose you tolerated if a new step is too rough.

Missed dose: take it within 4 days, otherwise skip it and carry on. Pill contraception: tirzepatide can make it less reliable, so the label advises adding a barrier method for 4 weeks after starting and after each increase⁴.

Preparing & storing

Branded pens and vials stay in the fridge (2–8 °C), never frozen, and can be kept at room temperature for a limited time according to the label. Lyophilised research material is reconstituted with bacteriostatic water, swirled rather than shaken, refrigerated and kept out of light. Inject into the abdomen, thigh or upper arm on the same weekday each week, rotating sites. Meal timing doesn't matter.

Known side effects

Nausea, the most common, reported by roughly a quarter to a third of people on higher doses in trials, mostly during dose increases
Diarrhoea, vomiting, constipation
Gallbladder problems, linked to rapid weight loss
Loss of lean mass when protein intake and resistance training are neglected
Mild injection-site reactions
Rare: pancreatitis. Boxed warning for thyroid C-cell tumours seen in rodents.

Who should avoid it

Personal or family history of medullary thyroid cancer, or MEN2
History of pancreatitis, unless under specialist care
Pregnancy, or trying to conceive
Severe gastrointestinal disease (use caution)
Do not combine with semaglutide, retatrutide or other incretin drugs
Insulin or sulfonylurea users need those doses reviewed because of hypoglycaemia risk

Tracking progress

Measure	Why	When
Weight & waist	The main outcome	Baseline, then weekly
Fasting glucose, HbA1c	Metabolic effect	Baseline, then every 8–12 weeks
Lipids, blood pressure	Cardiometabolic picture	Baseline, then periodically
Strength or lean mass	Protects against muscle loss	Baseline, then periodically

Regulatory status checked Oct 2026

Body	Status	Detail
FDA (US)	Approved	Mounjaro (T2D); Zepbound (weight management, OSA). Prescription only.
EMA (EU)	Approved	Type 2 diabetes and weight management.
CDSCO (India)	Approved	Mounjaro launched and available.
WADA	Not prohibited	Incretin agonists are not on the prohibited list.

The NexGen read

The benchmark everything else is measured against

Tirzepatide has the strongest evidence in this guide. It produces large, durable weight loss and real metabolic benefit, and it beat semaglutide head to head. It only works while you take it, alongside high protein intake and resistance training. Titrate slowly, because nearly every side effect gets worse when doses go up too fast.

References

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. doi:10.1056/NEJMoa2206038
Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5). N Engl J Med. 2025;393:26–36.
Jastreboff AM, le Roux CW, Stefanski A, et al. Tirzepatide for obesity treatment and diabetes prevention. N Engl J Med. 2025;392:958–971.
Eli Lilly. Zepbound and Mounjaro (tirzepatide) prescribing information. Dosing, contraception interaction, boxed warning.