Skip to content
Easy Peptide Info
Menu
Approved medicine

What is tirzepatide?

Tirzepatide explained in plain English: what it is, what the research shows, side effects, legal status and dosage, plus a calculator for syringe units. Doses shown come only from the label or published trials, each with its source. Also called Mounjaro, Zepbound, Tirz.

Tirzepatide is a prescription medicine. This page is educational; use it only as prescribed by a qualified healthcare professional.

Calculate
Vial unit

= 10,000 mcg

mL
Dose unit
Syringe type
Syringe size

Units to draw

–units

Enter your dose.

Syringe, no result yetU-100, 1 mL syringe holding up to 100 units. Enter your dose.0102030405060708090100

Saved calculations

No saved calculations yet. Save one from the results.

What is tirzepatide?

Tirzepatide is a prescription medicine made by Eli Lilly that copies two gut hormones, GIP and GLP-1. It is the active ingredient in Mounjaro and Zepbound.

It is a peptide of 39 amino acids with a fatty side chain that keeps it in the body for about a week, so it is injected once a week.

What is tirzepatide used for?

Tirzepatide is FDA-approved for type 2 diabetes (Mounjaro, since 2022) and for long-term weight management (Zepbound, since 2023). In December 2024 Zepbound was also approved for moderate to severe obstructive sleep apnea in adults with obesity.

How does tirzepatide work?

Tirzepatide turns on both GIP and GLP-1 receptors. Together they boost insulin when blood sugar is high, slow stomach emptying and reduce appetite through the brain.

Acting on two hormone pathways instead of one is thought to explain why it produces more weight loss than GLP-1-only medicines.

What do the tirzepatide trials show?

In SURMOUNT-1, adults with obesity lost an average of up to 20.9% of their body weight over 72 weeks on the highest-strength tirzepatide, compared with about 3% on placebo. In the head-to-head SURMOUNT-5 trial, tirzepatide led to 20.2% average weight loss versus 13.7% with semaglutide.

As with other medicines in this class, much of the weight tends to return after stopping.

Tirzepatide side effects

The most common side effects are nausea, diarrhea, vomiting, constipation, indigestion and stomach pain, mostly while the dose is being increased. Injection-site reactions and tiredness are also reported.

Serious risks include pancreatitis, gallbladder disease, kidney injury from dehydration and low blood sugar with insulin or some other diabetes medicines. Like semaglutide, it has a boxed warning about thyroid C-cell tumors seen in rodents, and it can make birth control pills less reliable for a while after starting or raising the dose.

Mostly not anymore. Compounded copies were allowed while tirzepatide was in shortage, which the FDA declared over in December 2024, and courts have backed that decision.

In April 2026 the FDA proposed removing tirzepatide from the list of ingredients large compounding facilities can use. “Research” tirzepatide sold online is not approved for human use and isn’t checked for purity or strength.

How much does tirzepatide cost?

US list prices for Mounjaro and Zepbound are over a thousand dollars a month before insurance. Lilly also sells Zepbound vials directly at lower cash-pay prices, and insurance coverage for weight loss varies.

How do you reconstitute tirzepatide?

Mounjaro and Zepbound pens and vials come as ready-to-use liquid, so they’re never mixed. If you have a powder vial, the calculator above turns the vial size, the bacteriostatic water and a dose into syringe units, and the reconstitution guide explains each step.

See the dosage section below for what is known about doses, with sources.

Tirzepatide dosage

Tirzepatide starts at 2.5 mg once a week for 4 weeks, then goes up in 2.5 mg steps no sooner than every 4 weeks. Zepbound and Mounjaro use the same steps; the maintenance dose depends on what it is treating.

From the official prescribing information (label). Your prescriber decides your dose and when to change it.

Tirzepatide doses, with sources
WhenDoseHow often
Weeks 1–4 (start only, not a maintenance dose)2.5 mg[1]Once a week
From week 55 mg[1]Once a week
Increases, if needed+2.5 mg after at least 4 weeks on the current dose[1]Once a week
Zepbound maintenance, weight5 mg, 10 mg or 15 mg[1]Once a week
Zepbound maintenance, sleep apnea10 mg or 15 mg[1]Once a week
Mounjaro (type 2 diabetes), maximum15 mg[2]Once a week
  1. Eli Lilly, Zepbound prescribing information
  2. Eli Lilly, Mounjaro prescribing information

Medical disclaimer: this dosage information is for education only and comes from the source shown for each row. It is not medical advice and not a recommendation for you. Only a licensed prescriber who knows your health can decide whether Tirzepatide is right for you and at what dose. Don't start, change or stop a medicine based on this page, and don't use research peptides or unapproved drugs based on trial doses.

Tirzepatide concentration chart

The concentration of a Tirzepatide vial depends only on its size and the water you add. Each unit on a U-100 syringe holds one hundredth of a mL.

Tirzepatide concentration by vial size and water
Vial + waterConcentrationPer unit (U-100)
10 mg + 1 mL10,000 mcg/mL (10 mg/mL)100 mcg per unit (0.1 mg per unit)
10 mg + 2 mL5,000 mcg/mL (5 mg/mL)50 mcg per unit (0.05 mg per unit)
10 mg + 3 mL3,333.33 mcg/mL (3.33333 mg/mL)33.33 mcg per unit (0.03333 mg per unit)
20 mg + 1 mL20,000 mcg/mL (20 mg/mL)200 mcg per unit (0.2 mg per unit)
20 mg + 2 mL10,000 mcg/mL (10 mg/mL)100 mcg per unit (0.1 mg per unit)
20 mg + 3 mL6,666.67 mcg/mL (6.66667 mg/mL)66.67 mcg per unit (0.06667 mg per unit)
30 mg + 1 mL30,000 mcg/mL (30 mg/mL)300 mcg per unit (0.3 mg per unit)
30 mg + 2 mL15,000 mcg/mL (15 mg/mL)150 mcg per unit (0.15 mg per unit)
30 mg + 3 mL10,000 mcg/mL (10 mg/mL)100 mcg per unit (0.1 mg per unit)

Frequently asked questions

Is tirzepatide the same as Mounjaro?

Tirzepatide is the medicine inside Mounjaro and Zepbound. Mounjaro is approved for type 2 diabetes, and Zepbound for weight management and obstructive sleep apnea.

Is tirzepatide better than semaglutide?

For weight loss, the head-to-head SURMOUNT-5 trial found more average weight loss with tirzepatide (20.2%) than semaglutide (13.7%) at 72 weeks. Which is better for a given person depends on side effects, cost and health conditions.

Is tirzepatide a GLP-1?

Partly. It acts on GLP-1 receptors and also on GIP receptors, so it's called a dual agonist.

Is compounded tirzepatide legal?

The shortage that allowed copies ended in December 2024. In April 2026 the FDA proposed removing tirzepatide from the list large compounders can use, which would close most remaining compounding.

Sources

  1. Jastreboff et al. (2022), Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1), New England Journal of Medicine
  2. American College of Cardiology (2025), SURMOUNT-5 journal scan
  3. Medscape (2026), FDA Proposes End to Mass GLP-1 Compounding

Last updated .

More peptide guides and calculators