What Is Tirzepatide? How It Works, What It Treats and Side Effects

Tirzepatide is a once-weekly injection that acts on two gut hormone receptors at once. Here is what it does, which brands contain it, what the big trials found and what to watch for.

Medically informed guide · Updated October 2026 · 10 min read

Tirzepatide is a prescription medicine given as a shot under the skin once a week. It was the first medicine to activate two hormone receptors, GIP and GLP-1, which helps lower blood sugar, reduce appetite and support weight loss. In the U.S. it is sold as Mounjaro for type 2 diabetes and Zepbound for weight management and obstructive sleep apnea.

Type of medicine: a dual GIP and GLP-1 receptor agonist.
How it is taken: one injection under the skin, once a week, any time of day.
Brand names: Mounjaro (approved 2022) and Zepbound (approved 2023).
Average weight loss in the main obesity trial: 15% to 21% of body weight over 72 weeks, depending on dose.
Most common side effects: nausea, diarrhea, vomiting and constipation, mostly while the dose is being raised.
Not for people with a personal or family history of medullary thyroid cancer or MEN 2.

Bottom line: Tirzepatide is one of the most effective weight-loss and blood sugar medicines available today, but it is a long-term prescription with real side effects, so it starts at a low dose and goes up slowly under a provider's care.

Tirzepatide in plain English

Tirzepatide (pronounced tir-ZEP-a-tide, and sometimes misspelled trizepatide or tirzepitide) is a lab-made version of a hormone signal your gut already sends after you eat. It is a single molecule that turns on the receptors for two of those hormones: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1).

Older medicines in this family, like semaglutide, act on GLP-1 only. When the FDA approved tirzepatide in 2022, Lilly described it as the first and only approved medicine that acts on both GIP and GLP-1 receptors. That "dual" action is the main thing that sets it apart.

It is a weekly injection, not a daily pill. If you have seen talk about a tirzepatide tablet, our guide on whether there is a tirzepatide pill explains what exists and what does not.

How tirzepatide works

GIP and GLP-1 are called incretins. Your gut releases them when food arrives, and they tell the body how to handle the meal. Tirzepatide copies that signal and makes it last all week. In practice, that does several things:

Helps the pancreas release insulin when blood sugar is high. Because this depends on glucose, low blood sugar is uncommon unless you also take insulin or a sulfonylurea.
Lowers glucagon, a hormone that raises blood sugar.
Slows how fast the stomach empties, so you feel full longer after a meal.
Acts on appetite centers in the brain, so many people feel less hungry and think about food less.

Eating less, feeling full sooner and better blood sugar control together explain most of the weight loss people see. Researchers are still studying exactly how much the GIP part adds on top of GLP-1.

Brand names and what each is approved for

Both brands are made by Eli Lilly and contain the same active ingredient. They differ in what the FDA approved them to treat, and they should not be used together.

Brand	First FDA approval	Approved uses (with diet and exercise)	Dose range
Mounjaro	May 2022	Blood sugar control in type 2 diabetes (adults and children 10 and older); lowering the risk of heart attack, stroke and cardiovascular death in adults with type 2 diabetes at high risk	2.5 mg to 15 mg weekly (10 mg max for children)
Zepbound	November 2023	Chronic weight management in adults with a BMI of 30 or more, or 27 or more with a weight-related condition; moderate to severe obstructive sleep apnea in adults with obesity (added December 2024)	2.5 mg to 15 mg weekly

Mounjaro is not approved for weight loss on its own, although people taking it often lose weight. When the FDA approved Zepbound for sleep apnea in December 2024, it called it the first drug treatment option for certain patients with obstructive sleep apnea.

What the main trials found

Tirzepatide has been tested in large, randomized trials. Here are the ones that matter most for everyday questions.

Trial	Who was in it	Main result
SURMOUNT-1 (NEJM, 2022)	2,539 adults with obesity or overweight, no diabetes, 72 weeks	Average weight change of -15.0% (5 mg), -19.5% (10 mg) and -20.9% (15 mg), versus -3.1% with placebo
SURPASS-2 (NEJM, 2021)	1,879 adults with type 2 diabetes, 40 weeks	A1C fell 2.01 to 2.30 points with tirzepatide versus 1.86 points with semaglutide 1 mg; weight loss was also greater
SURMOUNT-OSA (NEJM, 2024)	Adults with moderate to severe sleep apnea and obesity, 52 weeks	Breathing pauses (AHI) dropped by about 25 to 29 events per hour, versus about 5 with placebo
SURMOUNT-5 (NEJM, 2025)	751 adults with obesity, no diabetes, 72 weeks, head-to-head	Average weight change of -20.2% with tirzepatide versus -13.7% with semaglutide

In SURMOUNT-1, about half of people on the 10 mg dose and 57% on the 15 mg dose lost 20% or more of their body weight, compared with 3% on placebo. Results vary a lot from person to person, and people with type 2 diabetes tend to lose somewhat less. For a deeper comparison with the other big option, see semaglutide vs tirzepatide.

💡 What "average" means here

Trial numbers are averages over more than a year, alongside diet and activity coaching. Some people lose much more, some much less, and weight often comes back if the medicine is stopped.

How it is taken and the dose range

Tirzepatide is injected under the skin of the belly, thigh or upper arm once a week, on the same day each week, with or without food. Rotate the spot each time.

Start low: 2.5 mg once a week for 4 weeks. This first dose is only for getting your body used to the medicine, not for long-term use.
Step up slowly: the dose can go up by 2.5 mg after at least 4 weeks on the current dose.
Maintenance: 5 mg, 10 mg or 15 mg once a week for weight management (10 mg or 15 mg for sleep apnea). The highest dose is 15 mg weekly.
Missed a dose? Take it within 4 days (96 hours). If more than 4 days have passed, skip it and take the next one on your usual day.
Changing your shot day is fine as long as doses are at least 3 days (72 hours) apart.

Not everyone needs to reach 15 mg. Many people stay at a lower dose that works and that they tolerate. Our tirzepatide dosage guide walks through each step and when providers usually move up.

Side effects and the boxed warning

Common side effects listed on the FDA label include nausea, diarrhea, vomiting, constipation, belly pain, indigestion, decreased appetite, burping, injection site reactions, tiredness, hair loss and acid reflux. In SURMOUNT-1 most stomach side effects were mild to moderate and happened mainly while the dose was being raised. Side effects led 4% to 7% of people on tirzepatide to stop, versus about 3% on placebo.

Serious but less common risks on the label include:

Pancreatitis (severe belly pain that may spread to the back)
Gallbladder problems, including gallstones
Kidney injury, usually from dehydration after vomiting or diarrhea
Severe stomach problems; not recommended for people with severe gastroparesis
Serious allergic reactions, including swelling of the face or throat
Low blood sugar, mainly when combined with insulin or a sulfonylurea
Worsening diabetic eye disease in people with type 2 diabetes
Breathing food into the lungs during anesthesia or deep sedation, so tell your surgical team you take it

⚠️ The boxed warning: thyroid C-cell tumors

Tirzepatide caused thyroid C-cell tumors in rats. It is not known whether it does this in people. Because of that, it must not be used by anyone with a personal or family history of medullary thyroid carcinoma (MTC) or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Tell your provider about a lump or swelling in your neck, hoarseness, trouble swallowing or shortness of breath.

Birth control pills: tirzepatide can make oral contraceptives less reliable. The label advises switching to a non-pill method, or adding a barrier method, for 4 weeks after starting and for 4 weeks after each dose increase.

Who should not take tirzepatide

Anyone with a personal or family history of medullary thyroid cancer, or with MEN 2
Anyone who has had a serious allergic reaction to tirzepatide or its ingredients
Anyone already taking another tirzepatide product or a GLP-1 medicine
People with type 1 diabetes (it is not approved for type 1)
People who are pregnant, trying to get pregnant or breastfeeding should talk with their provider first

Also tell your provider if you have had pancreatitis, gallbladder disease, kidney problems, severe stomach or bowel problems, or diabetic eye disease.

What brand-name tirzepatide costs

The cheapest path depends on your coverage, so check these first:

If your insurance covers it: the Mounjaro and Zepbound savings cards from Lilly can bring a covered fill down to as little as $25 for eligible people with commercial insurance.
If you pay cash for Zepbound: LillyDirect self-pay pricing starts at $299 a month for the 2.5 mg KwikPen or vials, and Lilly lists higher doses at higher prices (up to $699 a month), with a self-pay savings card that lowers some doses further.
If commercial insurance does not cover Mounjaro: the savings card lists prices as low as $499 for a 1-month fill.
If you have Medicare Part D: the Medicare GLP-1 Bridge pilot (July 2026 through December 2027) covers the Zepbound KwikPen for eligible people with a $50 monthly copay.

Lilly's card terms change often and currently expire December 31, 2026, so confirm the current price on lilly.com before you fill. For a dose-by-dose breakdown, see Zepbound cost by dose.

What about compounded tirzepatide?

Compounded tirzepatide is made by a licensed pharmacy for an individual patient's prescription. It contains the same molecule, but compounded medications are not FDA-approved, and they are not the same as any brand-name medication. The FDA does not review compounded drugs for safety, effectiveness or quality before they are sold.

The FDA removed tirzepatide from its drug shortage list in December 2024. State-licensed 503A pharmacies may still compound tirzepatide for an individual patient when a prescriber documents a clinical need, such as a dose or formulation that an approved product does not offer. The FDA also warns about unapproved GLP-1 products sold online, including fake products with false pharmacy names, so only use a state-licensed pharmacy with a real prescription.

Learn more in our guide to compounded tirzepatide.

Getting treatment through Rx.com

Rx.com offers compounded tirzepatide from $149/month on a 12-month plan, with an online provider visit, medication, supplies and cold shipping included. It is one flat price at every dose, and no insurance is needed.

Compounded medications are not FDA-approved. A licensed provider reviews your health history to decide whether tirzepatide is right for you. If you are not sure where to start, our weight-loss check takes a few minutes.

🚨 When to Contact Your Healthcare Provider

Call your provider right away if any of these happen. Call 911 for trouble breathing, fainting or severe pain.

Severe belly pain that will not go away, with or without vomiting, especially if it spreads to your back: possible pancreatitis.
Pain in the upper right belly, fever, or yellow skin or eyes: possible gallbladder problem.
Vomiting or diarrhea that keeps you from drinking fluids: risk of dehydration and kidney injury.
Swelling of the face, lips or throat, hives or trouble swallowing: possible allergic reaction.
A lump in the neck, hoarseness or trouble swallowing: tell your provider promptly.
Shakiness, sweating, confusion or a fast heartbeat: possible low blood sugar, especially with insulin.
Changes in vision if you have diabetes.

Frequently Asked Questions

What is tirzepatide used for?

It is approved to improve blood sugar in type 2 diabetes, to lower heart risk in some adults with type 2 diabetes, for chronic weight management, and for moderate to severe obstructive sleep apnea in adults with obesity.

Is tirzepatide the same as Mounjaro and Zepbound?

Yes. Tirzepatide is the active ingredient in both. Mounjaro is the brand for type 2 diabetes and Zepbound is the brand for weight management and sleep apnea.

Is tirzepatide a GLP-1?

It is a GLP-1 receptor agonist and a GIP receptor agonist in one molecule, which is why it is called a dual agonist.

How much weight do people lose on tirzepatide?

In the SURMOUNT-1 trial, adults without diabetes lost an average of 15% to 21% of their body weight over 72 weeks, depending on dose, versus about 3% on placebo.

How long does it take to work?

Appetite changes often start in the first weeks, but weight loss builds slowly as the dose rises every 4 weeks or more. In trials, weight kept falling for well over a year.

Is tirzepatide stronger than semaglutide?

In the SURMOUNT-5 head-to-head trial, people on tirzepatide lost more weight on average (20.2% versus 13.7%). Which one suits you depends on your health, side effects and cost.

Is there a generic tirzepatide?

No. There is no FDA-approved generic version of tirzepatide in the U.S.

How is trizepatide spelled?

The correct spelling is tirzepatide. Trizepatide and tirzepitide are common misspellings of the same medicine.

Rx.com Weight Loss Program

GLP-1 treatment from $99/month, prescribed online by a licensed U.S. provider

Compounded Tirzepatide

Weekly GLP-1 + GIP injection

$149/mo

with a 12-month plan

Compounded Semaglutide

Weekly GLP-1 injection

$99/mo