Tirzepatide
GLP-1/GIP Dual Receptor Agonist for Type 2 Diabetes and Weight Loss
Quick Facts About Tirzepatide
Key Takeaways About Tirzepatide
- First dual-action incretin: Tirzepatide is the first medication to activate both GIP and GLP-1 receptors, delivering superior blood sugar control and weight loss compared to GLP-1-only drugs
- Remarkable weight loss: Clinical trials demonstrated up to 22.5% body weight reduction (SURMOUNT-1), the highest ever recorded for a non-surgical weight loss treatment
- Two approved indications: Mounjaro for type 2 diabetes and Zepbound for chronic weight management in adults with obesity or overweight with comorbidities
- Gradual dose escalation required: Start at 2.5 mg weekly and increase every 4 weeks to minimise gastrointestinal side effects such as nausea and vomiting
- Thyroid cancer warning: Not recommended in patients with a personal or family history of medullary thyroid carcinoma or MEN 2 syndrome, based on animal study findings
What Is Tirzepatide and What Is It Used For?
Tirzepatide is a first-in-class dual GIP/GLP-1 receptor agonist used to treat type 2 diabetes (as Mounjaro) and chronic weight management/obesity (as Zepbound). It is a once-weekly subcutaneous injection that lowers blood sugar, reduces appetite, and produces significant weight loss.
Tirzepatide represents a breakthrough in metabolic medicine as the first medication to simultaneously activate two incretin hormone receptors: the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor. This dual mechanism of action sets it apart from existing GLP-1 receptor agonists such as semaglutide and liraglutide, which target only the GLP-1 receptor.
For type 2 diabetes, tirzepatide is marketed under the brand name Mounjaro. It improves blood sugar control by enhancing insulin secretion when glucose levels are high, suppressing glucagon release, and slowing the rate at which food leaves the stomach. In the SURPASS clinical trial programme, tirzepatide reduced HbA1c (a measure of long-term blood sugar control) by up to 2.58 percentage points – more than any other injectable diabetes medication studied.
For chronic weight management, tirzepatide is marketed as Zepbound. It is approved for adults with obesity (BMI of 30 or higher) or overweight (BMI of 27 or higher) who also have at least one weight-related medical condition, such as high blood pressure, dyslipidaemia, type 2 diabetes, obstructive sleep apnoea, or cardiovascular disease. In the SURMOUNT-1 trial, participants without diabetes lost an average of 22.5% of their body weight on the highest dose – an unprecedented result for a pharmaceutical treatment.
Tirzepatide is not indicated for the treatment of type 1 diabetes. It has not been studied in patients with a history of pancreatitis, and its use in such patients is not recommended.
Tirzepatide was first approved by the U.S. FDA in May 2022 for type 2 diabetes (Mounjaro) and in November 2023 for weight management (Zepbound). The European Medicines Agency (EMA) approved Mounjaro in September 2022. It is a synthetic peptide of 39 amino acids, engineered from the native GIP sequence with modifications that enable GLP-1 receptor activation and a long half-life suitable for once-weekly dosing.
What Should You Know Before Taking Tirzepatide?
Before starting tirzepatide, inform your doctor about any history of pancreatitis, thyroid tumours, kidney disease, diabetic retinopathy, or gallbladder problems. Tirzepatide is contraindicated in patients with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
Contraindications
You should not take tirzepatide if any of the following apply to you:
- Personal or family history of medullary thyroid carcinoma (MTC) – in animal studies, GLP-1 receptor agonists caused thyroid C-cell tumours. While relevance to humans is uncertain, tirzepatide carries a boxed warning regarding this risk
- Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) – patients with this genetic condition are at increased risk of medullary thyroid cancer
- Known hypersensitivity to tirzepatide or any of the excipients – serious hypersensitivity reactions including anaphylaxis and angioedema have been reported
- Type 1 diabetes – tirzepatide is not a substitute for insulin and should not be used in type 1 diabetes
Warnings and Precautions
Talk to your doctor before taking tirzepatide if you have or have had any of the following conditions:
- History of pancreatitis – tirzepatide has not been studied in patients with prior pancreatitis. Discontinue immediately if pancreatitis is suspected (severe abdominal pain that may radiate to the back, with or without vomiting)
- Diabetic retinopathy – rapid improvement of glucose control has been associated with temporary worsening of diabetic retinopathy. Patients with a history of diabetic retinopathy should be monitored closely
- Gallbladder disease – GLP-1 receptor agonists are associated with an increased risk of gallstones (cholelithiasis) and gallbladder inflammation (cholecystitis), particularly with substantial weight loss
- Severe kidney disease – gastrointestinal side effects (nausea, vomiting, diarrhoea) can cause dehydration, which may worsen kidney function. Monitor renal function in patients with kidney disease
- Gastroparesis or severe gastrointestinal disease – tirzepatide slows gastric emptying, which may worsen pre-existing gastroparesis
Pregnancy and Breastfeeding
Tirzepatide should not be used during pregnancy. Animal studies have shown adverse effects on foetal development. Women of childbearing potential should use effective contraception while taking tirzepatide. Because tirzepatide delays gastric emptying, it may reduce the effectiveness of oral contraceptives – consult your doctor about switching to a non-oral method or using a back-up barrier method.
Discontinue tirzepatide at least 2 months before a planned pregnancy, given the drug's long washout period. It is unknown whether tirzepatide passes into breast milk. Due to the lack of safety data, breastfeeding is not recommended during treatment.
In rodent studies, tirzepatide caused dose-dependent thyroid C-cell tumours, including medullary thyroid carcinoma. It is unknown whether tirzepatide causes thyroid C-cell tumours in humans. Tirzepatide is contraindicated in patients with a personal or family history of medullary thyroid carcinoma or MEN 2. Counsel patients regarding the potential risk and symptoms of thyroid tumours (a lump in the neck, hoarseness, difficulty swallowing, or shortness of breath).
How Does Tirzepatide Interact with Other Drugs?
Tirzepatide delays gastric emptying, which can affect the absorption of oral medications taken at the same time. Insulin and sulfonylurea doses must be reduced when starting tirzepatide to avoid hypoglycaemia. Always inform your doctor about all medications you are taking.
Unlike many drugs that interact through liver enzyme pathways, tirzepatide's most clinically significant interactions result from its effect on delayed gastric emptying. By slowing the rate at which food and medications leave the stomach, tirzepatide can alter the absorption rate and peak blood levels of certain oral drugs, particularly those that rely on rapid absorption for their effect.
| Drug | Category | Effect | Recommendation |
|---|---|---|---|
| Insulin | Antidiabetic | Additive blood sugar lowering; high risk of hypoglycaemia | Reduce insulin dose by 20% when starting tirzepatide; monitor blood glucose closely and titrate |
| Sulfonylureas (glipizide, glimepiride, glyburide) | Antidiabetic | Increased risk of hypoglycaemia | Consider reducing sulfonylurea dose when initiating tirzepatide; monitor blood glucose |
| Oral contraceptives | Hormonal contraception | Delayed gastric emptying may reduce absorption and effectiveness | Switch to non-oral contraception or add a barrier method; take the pill at least 1 hour before tirzepatide injection day |
| Warfarin | Anticoagulant | Delayed absorption may alter INR control | Monitor INR more frequently when starting or changing tirzepatide dose |
| Levothyroxine | Thyroid hormone | Delayed gastric emptying may reduce absorption | Take levothyroxine on an empty stomach at least 30–60 minutes before any food or other medication; monitor thyroid function |
| Antibiotics (e.g. amoxicillin, ciprofloxacin) | Anti-infective | Delayed absorption may reduce peak concentration of time-sensitive antibiotics | Monitor for adequate treatment response; consider parenteral antibiotics for severe infections |
When adding tirzepatide to existing insulin therapy, the insulin dose must be reduced to prevent potentially dangerous hypoglycaemia (low blood sugar). Your doctor will guide you on how much to reduce. Typical guidance is to reduce basal insulin by approximately 20% when starting tirzepatide, with further adjustments based on blood glucose monitoring. Signs of hypoglycaemia include shakiness, sweating, rapid heartbeat, dizziness, confusion, and hunger.
Tirzepatide can generally be used safely alongside metformin and SGLT2 inhibitors (such as empagliflozin or dapagliflozin) without dose adjustments. However, always tell your doctor about all medications you are taking, including over-the-counter products, vitamins, and herbal supplements.
What Is the Correct Dosage of Tirzepatide?
Tirzepatide is started at 2.5 mg once weekly and increased by 2.5 mg every 4 weeks to reach the target maintenance dose. The maximum dose is 15 mg once weekly. It is injected subcutaneously in the abdomen, thigh, or upper arm.
Tirzepatide uses a gradual dose-escalation schedule designed to minimise gastrointestinal side effects, particularly nausea. The starting dose of 2.5 mg is not a therapeutic dose – it is an initiation dose to help your body adjust to the medication. Always follow your doctor's prescribed dose schedule.
Dose Escalation Schedule
Standard Titration (Both Indications)
Weeks 1–4: 2.5 mg once weekly (initiation dose)
Weeks 5–8: 5 mg once weekly
Weeks 9–12: 7.5 mg once weekly (if tolerated)
Weeks 13–16: 10 mg once weekly (if tolerated)
Weeks 17–20: 12.5 mg once weekly (if tolerated)
Week 21 onwards: 15 mg once weekly (maximum dose, if tolerated)
The dose may be increased in 2.5 mg increments no more frequently than every 4 weeks. Your doctor will determine the optimal maintenance dose based on your glycaemic response, weight loss goals, and tolerability.
Type 2 Diabetes (Mounjaro)
Maintenance dose range: 5 mg, 10 mg, or 15 mg once weekly
Many patients achieve adequate blood sugar control at 5 mg or 10 mg. The dose is titrated based on HbA1c targets and tolerability.
Chronic Weight Management (Zepbound)
Maintenance dose range: 5 mg, 10 mg, or 15 mg once weekly
Higher doses generally produce greater weight loss. The goal is to reach the maximum tolerated dose for optimal results.
How to Inject
Tirzepatide is supplied in a single-dose pre-filled pen with a hidden needle. Inject subcutaneously (under the skin) into your:
- Abdomen (at least 5 cm away from the navel)
- Thigh (front or outer side)
- Upper arm (outer area, if someone else is giving the injection)
Rotate injection sites with each weekly dose. Do not inject into the same exact spot each time. Inject on the same day each week, at any time of day, with or without food. If you need to change your injection day, ensure at least 3 days (72 hours) have passed since your last injection.
Missed Dose
If you miss a dose, take it as soon as possible within 4 days (96 hours) of the missed dose. If more than 4 days have passed, skip the missed dose and take your next scheduled dose on the regular day. Do not take two doses within 3 days of each other.
What Are the Side Effects of Tirzepatide?
The most common side effects of tirzepatide are gastrointestinal: nausea (up to 31%), diarrhoea, vomiting, constipation, and decreased appetite. These are usually most pronounced during dose escalation and tend to diminish over time. Rare but serious risks include pancreatitis, gallbladder disease, and thyroid tumours (observed in animals).
Like all medicines, tirzepatide can cause side effects, although not everybody gets them. Gastrointestinal side effects are the most frequently reported and are generally mild to moderate in severity. They are most common during the dose-escalation phase and tend to decrease as the body adjusts to each new dose level.
- Severe, persistent abdominal pain that may radiate to the back (possible pancreatitis)
- A lump or swelling in the neck, hoarseness, difficulty swallowing (possible thyroid tumour)
- Signs of a severe allergic reaction: rash, itching, swelling of face/lips/tongue/throat, difficulty breathing
- Signs of severe hypoglycaemia: confusion, loss of consciousness, seizures (especially if taking insulin or sulfonylureas)
- Severe pain in the upper right abdomen, fever, clay-coloured stools (possible gallbladder disease)
Very Common
May affect more than 1 in 10 people
- Nausea (up to 31% at higher doses, especially during dose escalation)
- Diarrhoea
- Decreased appetite
- Vomiting
- Constipation
Common
May affect up to 1 in 10 people
- Abdominal pain and dyspepsia (indigestion)
- Injection site reactions (redness, itching, pain at injection site)
- Fatigue
- Gastro-oesophageal reflux disease (heartburn, acid reflux)
- Abdominal distension (bloating)
- Eructation (belching)
- Flatulence
- Hair loss (alopecia, typically mild and temporary)
- Hypoglycaemia (when used with insulin or sulfonylureas)
- Dizziness
Uncommon
May affect up to 1 in 100 people
- Gallstones (cholelithiasis)
- Gallbladder inflammation (cholecystitis)
- Increased heart rate
- Increased lipase and/or amylase levels (pancreatic enzymes)
- Hypersensitivity reactions
Rare
May affect up to 1 in 1,000 people
- Acute pancreatitis
- Anaphylaxis or severe allergic reactions
- Angioedema
- Acute kidney injury (secondary to severe dehydration from GI side effects)
- Intestinal obstruction (in patients with pre-existing gastroparesis)
Most gastrointestinal side effects can be managed by following the recommended gradual dose escalation, eating smaller meals, avoiding high-fat or greasy foods, and staying well hydrated. If side effects are severe or persistent, your doctor may delay the next dose increase or reduce your dose temporarily.
How Should You Store Tirzepatide?
Store unused tirzepatide pens in the refrigerator at 2–8°C. A pen in use may be kept at room temperature (up to 30°C) for a maximum of 30 days. Do not freeze. Protect from light.
Before First Use
Store tirzepatide pens in the refrigerator at 2–8°C (36–46°F). Keep them in the original carton to protect from light. Do not freeze tirzepatide. If a pen has been accidentally frozen, do not use it – discard it and use a new pen.
After First Use / Room Temperature Storage
Each tirzepatide pen is a single-dose pen, so there is no multi-use storage concern. However, if you prefer to take a pen out of the refrigerator before your injection, it may be stored at room temperature up to 30°C (86°F) for a maximum of 30 days. Do not return a pen to the refrigerator once it has been stored at room temperature. Discard any pen that has been out of the refrigerator for more than 30 days.
Disposal
Dispose of used pens in an appropriate sharps disposal container. Do not throw pens in household waste or recycle them. Return full sharps containers to your pharmacy or local disposal facility. Check the expiry date before each injection and do not use a pen past its expiry date.
What Does Tirzepatide Contain?
Each tirzepatide pre-filled pen contains the active ingredient tirzepatide in a clear, colourless to slightly yellow solution for subcutaneous injection. Available strengths range from 2.5 mg to 15 mg per dose.
Active Ingredient
The active substance is tirzepatide, a synthetic peptide consisting of 39 amino acids. It is engineered from the human GIP peptide sequence with modifications that enable dual GIP and GLP-1 receptor activation and attachment to a C20 fatty diacid moiety that binds to albumin, extending its half-life to approximately 5 days for once-weekly dosing.
Inactive Ingredients (Excipients)
The other ingredients are: sodium chloride, sodium phosphate dibasic heptahydrate, hydrochloric acid (for pH adjustment), sodium hydroxide (for pH adjustment), and water for injections.
Sodium Content
This medicine contains less than 1 mmol (23 mg) sodium per dose, meaning it is essentially "sodium-free". This is relevant for patients on a sodium-restricted diet.
Pen Description and Packaging
Tirzepatide is supplied as a clear, colourless to slightly yellow solution in a single-dose pre-filled pen (KwikPen). Each pen delivers one fixed dose. The pen features a hidden needle to minimise injection anxiety. Available pack sizes include 2 or 4 pre-filled pens per carton, depending on the market and strength.
How Does Tirzepatide Work in the Body?
Tirzepatide is a dual GIP and GLP-1 receptor agonist that works through multiple mechanisms: it enhances glucose-dependent insulin secretion, suppresses glucagon, delays gastric emptying, and reduces appetite via the hypothalamus. This dual action produces superior glycaemic control and weight loss of 20–25% in clinical trials.
To understand how tirzepatide works, it is helpful to know about the incretin system. When you eat, your gut releases two key hormones: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). Together, these hormones are responsible for up to 70% of the insulin response to a meal – a phenomenon known as the incretin effect. In people with type 2 diabetes, this incretin effect is diminished.
Dual Receptor Activation
Tirzepatide mimics the actions of both GIP and GLP-1 simultaneously, producing complementary and synergistic effects:
- GLP-1 receptor activation: Enhances glucose-dependent insulin secretion from pancreatic beta cells, suppresses inappropriately elevated glucagon from alpha cells, delays gastric emptying, and promotes satiety (feeling of fullness) through central nervous system signalling in the hypothalamus
- GIP receptor activation: Further enhances insulin secretion, may improve beta-cell function, promotes fat metabolism, and appears to amplify the weight-loss effects of GLP-1 receptor activation through mechanisms still being investigated – including effects on adipose tissue and central appetite regulation
Weight Loss Mechanisms
Tirzepatide produces its remarkable weight loss through several complementary pathways:
- Appetite suppression: Both GIP and GLP-1 receptor signalling in the hypothalamus reduce hunger and increase satiety, leading to a natural reduction in caloric intake of approximately 20–35%
- Delayed gastric emptying: Food remains in the stomach longer, promoting prolonged feelings of fullness after meals
- Improved fat metabolism: GIP receptor activation may enhance lipid metabolism and reduce fat storage, particularly visceral (belly) fat
- Reduced food reward signalling: Evidence suggests that GLP-1 receptor agonists reduce the brain's reward response to food, decreasing cravings and food preoccupation
Pharmacokinetic Profile
After subcutaneous injection, tirzepatide reaches peak plasma concentrations in approximately 8–72 hours (median 24 hours). The half-life is approximately 5 days (120 hours), which supports once-weekly dosing. Bioavailability is approximately 80%. Tirzepatide is degraded by proteolytic cleavage, amide hydrolysis, beta-oxidation, and diketopiperazine formation. Metabolites are primarily excreted by the kidneys. Steady-state concentrations are reached after 4 weeks of weekly dosing.
Clinical Efficacy
The clinical evidence for tirzepatide is among the most impressive for any metabolic medication:
- SURPASS-2 (vs semaglutide 1 mg): Tirzepatide 15 mg reduced HbA1c by 2.46% vs 1.86% for semaglutide, and body weight by 12.4 kg vs 6.2 kg
- SURMOUNT-1 (obesity without diabetes): Tirzepatide 15 mg produced 22.5% body weight loss (24 kg average) over 72 weeks vs 2.4% with placebo
- SURMOUNT-2 (obesity with diabetes): 15.7% weight loss and 2.1% HbA1c reduction at highest dose over 72 weeks
Frequently Asked Questions About Tirzepatide
In the SURMOUNT-1 clinical trial, participants without diabetes who received the maximum dose of tirzepatide (15 mg) lost an average of 22.5% of their body weight – approximately 24 kg (52 lbs) – over 72 weeks. This is the highest weight loss ever achieved with a non-surgical medication. Results vary by dose: 5 mg produced about 15% weight loss, 10 mg about 19.5%, and 15 mg about 22.5%. Individual results depend on factors including diet, physical activity, starting weight, and adherence to the medication.
Tirzepatide is a dual GIP/GLP-1 receptor agonist, while semaglutide targets only the GLP-1 receptor. In the SURPASS-2 head-to-head trial, tirzepatide achieved greater reductions in both HbA1c (2.46% vs 1.86%) and body weight (12.4 kg vs 6.2 kg) compared to semaglutide 1 mg in type 2 diabetes. For weight loss, tirzepatide 15 mg produced approximately 22.5% weight loss (SURMOUNT-1) compared to about 15–17% for semaglutide 2.4 mg (STEP-1). Both are effective treatments, and the best choice depends on individual factors, tolerability, insurance coverage, and availability.
Tirzepatide is injected once weekly using a pre-filled, single-dose pen with a hidden needle. Choose an injection site on your abdomen (at least 5 cm from the navel), thigh, or upper arm. Clean the area with an alcohol swab, place the pen flat against your skin, press and hold the injection button until you hear a click, and hold for at least 10 seconds. Rotate your injection site each week. Inject on the same day each week, at any time of day, with or without food. If you need to change your injection day, allow at least 3 days (72 hours) between doses.
When you stop tirzepatide, its appetite-suppressing and metabolic effects gradually wear off over several weeks. The SURMOUNT-4 study showed that participants who switched from tirzepatide to placebo regained approximately two-thirds of the weight they had lost over the following year. Blood sugar levels in patients with type 2 diabetes also tend to rise back toward pre-treatment levels. For this reason, tirzepatide is generally considered a long-term treatment. If you wish to stop, discuss a gradual plan with your doctor to help maintain as many benefits as possible through lifestyle modifications.
Insurance coverage varies significantly. Mounjaro (for type 2 diabetes) is covered by many insurance plans and Medicare Part D, although prior authorisation may be required. Zepbound (for obesity and weight management) has more limited coverage because many insurance plans exclude weight loss medications. In Europe, national formulary coverage differs by country. Check with your specific insurance plan for current coverage details. The manufacturer (Eli Lilly) offers savings programmes and patient assistance in some markets to help reduce out-of-pocket costs.
Yes. Tirzepatide is approved under the brand name Zepbound specifically for chronic weight management in adults without diabetes. You must meet the eligibility criteria: a BMI of 30 or higher (obesity), or a BMI of 27 or higher (overweight) with at least one weight-related health condition such as high blood pressure, high cholesterol, heart disease, obstructive sleep apnoea, or type 2 diabetes. Zepbound should be used alongside a reduced-calorie diet and increased physical activity. Only a doctor can determine whether tirzepatide is appropriate for your individual situation.
References
This article is based on the following international medical guidelines and peer-reviewed sources. All medical claims have evidence level 1A, the highest quality of evidence based on systematic reviews of randomised controlled trials.
- Frias JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2). New England Journal of Medicine. 2021;385(6):503–515. doi:10.1056/NEJMoa2107519
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine. 2022;387(3):205–216. doi:10.1056/NEJMoa2206038
- Garvey WT, Frias JP, Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2). The Lancet. 2023;402(10402):613–626. doi:10.1016/S0140-6736(23)01200-X
- Aronne LJ, Sattar N, Horn DB, et al. Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity (SURMOUNT-4). JAMA. 2024;331(1):38–48. doi:10.1001/jama.2023.24945
- American Diabetes Association Professional Practice Committee. Standards of Care in Diabetes – 2026. Diabetes Care. 2026;49(Supplement 1):S1–S291.
- European Medicines Agency (EMA). Mounjaro (tirzepatide) – Summary of Product Characteristics. EMA product information database. Accessed March 2026.
- U.S. Food and Drug Administration (FDA). Mounjaro (tirzepatide) Prescribing Information. Revised 2025. Accessed March 2026.
- Rosenstock J, Wysham C, Frias JP, et al. Efficacy and safety of a novel dual GIP and GLP-1 receptor agonist tirzepatide in patients with type 2 diabetes (SURPASS-1). The Lancet. 2021;398(10295):143–155. doi:10.1016/S0140-6736(21)01324-6
Editorial Team
This article has been written and reviewed by the iMedic Medical Editorial Team, a group of licensed specialist physicians with expertise in endocrinology, obesity medicine, clinical pharmacology, and internal medicine.
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