Tirzepatid

Tirzepatide is a dual GLP-1/GIP receptor agonist (a "twincretin") - a synthetic peptide drug used to treat type 2 diabetes, obesity, and obstructive sleep apnea. Like semaglutide, tirzepatide belongs to the class of incretin mimetics, but it activates two metabolic gut hormones at the same time. In phase 3 clinical trials, tirzepatide leads to an average weight loss of over 20% and specifically reduces visceral belly fat. At the start of treatment, gastrointestinal issues such as nausea, vomiting, and diarrhea are very common.

How is tirzepatide used? Injection and forms

Tirzepatide is injected once a week subcutaneously (under the skin) into the abdomen, thigh, or upper arm - this is the only administration method that is clinically proven and approved by health authorities [1][2]. On the regular pharmaceutical market, tirzepatide is available as a ready-to-use single-dose pen (autoinjector), as a single-dose vial (since August 2024), as a multi-dose KwikPen (since February 2026), and as a multi-dose vial [1][2][10]. Single-dose vials and pens contain 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg per 0.5 mL; multi-dose vials and KwikPens deliver four doses of 0.6 mL from a total volume of 2.4 mL [2].

On the unregulated gray market outside of pharmacies, tirzepatide is usually sold as a lyophilized (freeze-dried) powder in vials of 5 to 120 mg, which must be manually reconstituted with sterile BAC water before injection. This unapproved use carries significant risks regarding sterility, purity, and the exact amount of active ingredient. You can find detailed criteria for quality checks and risk reduction in the guide on protection when ordering.

How do reconstitution and dose calculation work for tirzepatide?

Approved finished drugs like Mounjaro or Zepbound are ready-to-use solutions and don't need to be mixed, while gray-market lyophilisates must be manually dissolved with a solvent before injection. The following calculation example illustrates how to figure out the injection volume for a 30-mg vial and is not a recommendation for use:

• Vial: 30 mg tirzepatide (lyophilisate)
• Reconstitution: Add 3 mL BAC water -> concentration: 10 mg/mL
• 2.5 mg dose (starting dose): draw up 0.25 mL
• 5 mg dose: draw up 0.5 mL
• 15 mg dose (maximum): draw up 1.5 mL

You can determine the exact injection volume and the amount of active ingredient per dose with the injection calculator. Detailed step-by-step procedures for proper dissolving and safe handling are described in the instructions.

Storage: A tirzepatide solution reconstituted with BAC water must be stored in the refrigerator at 2-8 °C. Approved ready-to-use pens remain stable for a maximum of 21 days at room temperature up to 30 °C without refrigeration [1][2].

How tirzepatide works: What does the dual agonist do?

Tirzepatide acts as a dual receptor agonist by simultaneously mimicking the signals of the two natural gut hormones GLP-1 and GIP. The gut hormone GLP-1 (glucagon-like peptide-1) slows down stomach emptying and enhances the feeling of fullness in the brain, while GIP (glucose-dependent insulinotropic polypeptide) boosts the glucose-dependent release of insulin from the pancreas and improves insulin sensitivity, leading to stronger appetite control than with mono-agonists.

With a plasma half-life of about 5 days, tirzepatide allows for a weekly dosing interval with stable drug levels. A stable pharmacological steady state in the bloodstream is reached after about four weeks of regular use [1].

Approval and uses: What is tirzepatide approved for?

Tirzepatide has official drug approvals from the US FDA and the European EMA for three medical indications:

• Type 2 diabetes (brand name Mounjaro) - to lower blood sugar levels in adults [1]
• Obesity (brand name Zepbound) - for weight loss starting at a BMI >=30 or at a BMI >=27 with weight-related comorbidities [2]
• Obstructive sleep apnea (brand name Zepbound, since December 2024) - for adults with obesity and moderate to severe sleep apnea [3][9]

In the phase 3 approval trials, tirzepatide reduced body weight by an average of more than 20% and specifically decreased visceral fat tissue. At the start of treatment, gastrointestinal issues like nausea and diarrhea are typical side effects.

Tirzepatide vs. semaglutide: What does the study comparison show?

In direct clinical comparison, tirzepatide leads to significantly greater weight loss than semaglutide, which is a pure GLP-1 receptor agonist. This is supported by the phase 3 study programs SURPASS and SURMOUNT: In the direct head-to-head study SURMOUNT-5 (NEJM 2025, n=751), participants taking tirzepatide lost an average of 20.2% of their starting weight, compared to 13.7% for those taking semaglutide [4][7].

What side effects and risks does tirzepatide have?

Very common side effects of tirzepatide include dose-dependent gastrointestinal issues such as nausea, diarrhea, vomiting, constipation, and abdominal pain, which mainly occur during the dose-escalation phase. Additionally, there are the following clinically relevant risks:

• Gallbladder disease: Increased occurrence of cholelithiasis (gallstones) and cholecystitis (inflammation of the gallbladder)
• Pancreatitis: Rare inflammation of the pancreas. If you have severe abdominal pain, get it checked by a doctor immediately
• Hypoglycemia: Increased risk of low blood sugar, especially when also taking insulin or sulfonylureas
• Injection site reactions: Local redness, swelling, or itching at the injection site

Tirzepatide must not be used during pregnancy and is strictly contraindicated in patients with multiple endocrine neoplasia type 2 (MEN2) and in those with a personal or family history of medullary thyroid carcinoma [1][2].

The earlier FDA warning about suicidal behavior and suicidal thoughts was officially removed from the prescribing information in February 2026, as extensive analyses of the SURMOUNT studies showed no increased risk. At the same time, the agency adjusted the warnings about severe gastrointestinal reactions [2].

What does the dosing schedule for tirzepatide look like?

The official dosing schedule for tirzepatide (Mounjaro and Zepbound) follows a 4-week titration plan in 2.5 mg steps, starting at 2.5 mg and increasing up to a maximum dose of 15 mg [1][2]:

Each dose level is maintained for at least 4 weeks before increasing the dose. The regular maintenance dose is 5 mg, 10 mg, or 15 mg weekly, depending on individual tolerance. For the indication of obstructive sleep apnea, only 10 mg or 15 mg are approved as maintenance doses; a dose of 5 mg is not sufficient for this [2]. This information is for educational purposes only and is not a medical dosing recommendation.