Pronunciation: mown-JAHR-OH
Generic name: tirzepatide
Dosage form: single-dose pen (2.5 mg/0.5 mL, 5 mg/0.5 mL, 7.5 mg/0.5 mL, 10 mg/0.5 mL, 12.5 mg/0.5 mL, 15 mg/0.5 mL), single-dose vial (2.5 mg/0.5 mL, 5 mg/0.5 mL, 7.5 mg/0.5 mL, 10 mg/0.5 mL, 12.5 mg/0.5 mL, 15 mg/0.5 mL)
Drug class: GLP-1 receptor agonists

Medically reviewed by Carmen Pope, BPharm. Last updated on Sep 25, 2025.

What is Mounjaro?

Mounjaro is used for type 2 diabetes to help lower blood sugar levels. Mounjaro has also been shown to help with weight loss and maintain the lost weight in clinical trials when combined with diet and exercise. It is a once-weekly injection that can be self-administered and should be used alongside dietary changes and exercise.

Mounjaro works by activating two gut hormone receptors, GIP and GLP-1, to manage blood sugar. This stimulates insulin release when glucose is high, reduces liver glucagon production, slows stomach emptying to control post-meal sugar spikes, and increases fullness to reduce appetite and food intake. 

Mounjaro's dual mechanism of action makes it significantly more effective than semaglutide for weight loss, which only activates GLP-1 receptors, as demonstrated in the head-to-head Surmount-5 clinical trial (NCT05822830), which reported an overall 47% greater weight loss with tirzepatide (Mounjaro, Zepbound) compared to semaglutide.

• Weight loss: 20.2% with tirzepatide vs.13.7% with semaglutide
• Average weight loss: 50.3 lbs with tirzepatide vs. 33.1 lbs with semaglutide
• Waist circumference reduction: 7.2 inches with tirzepatide vs. 5.1 inches with semaglutide.

Mounjaro (tirzepatide) received FDA approval on May 13, 2022. There is no Mounjaro generic. The 2 different brands of tirzepatide (Mounjaro and Zepbound) are made by Eli Lilly and Company but are FDA-approved for different conditions.

• Mounjaro: Specifically approved for type 2 diabetes management in adults.
• Zepbound: Designated for weight loss treatment in adults.
• See Zepbound vs Mounjaro: Comparison Guide for Weight Loss and Diabetes Treatment.

What is the cost of Mounjaro?

The cost for prescription drugs varies depending on your insurance plan and which pharmacy you use. Refer to the Mounjaro price guide page for more cost information.

You may also be eligible for other savings. See "What is the Mounjaro Coupon or Savings Card?"

Mounjaro Side Effects: Guide to Tirzepatide Adverse Reactions

What are the Most Common Mounjaro Side Effects?

The most common side effects of Mounjaro (tirzepatide) are gastrointestinal and typically occur during the initial weeks of treatment. These tirzepatide side effects affect the digestive system and usually improve as your body adjusts to the medication.

Most Frequent Side Effects (Clinical Trials):

• Nausea (12-22% of patients) - most commonly reported
• Diarrhea (12-16% of patients)
• Decreased appetite (5-11% of patients)
• Vomiting (6-9% of patients)
• Constipation (6-7% of patients)
• Indigestion (dyspepsia) (4-7% of patients)
• Abdominal pain (4-6% of patients)
• Injection site reactions (pain, redness, swelling).

Timeline for Common Side Effects:

• Week 1-2: Peak intensity of gastrointestinal symptoms
• Week 3-4: Gradual improvement begins
• Week 4-8: Most patients experience a significant reduction in side effects
• After 8 weeks: Side effects are typically minimal or resolved.

Related/similar drugs

Serious Mounjaro Side Effects and FDA Boxed Warning

FDA Boxed Warning: Thyroid Cancer Risk

Mounjaro comes with an FDA Boxed warning that the drug has caused both cancerous and non-cancerous thyroid tumors in mice and rats. While the human risk remains unknown, patients should watch for these thyroid cancer symptoms:

Thyroid tumor warning signs:

• Lump or swelling in your neck
• Hoarseness that doesn't improve
• Trouble swallowing or breathing
• Shortness of breath
• Persistent cough without illness.

Do NOT use Mounjaro if you have:

• Personal or family history of medullary thyroid carcinoma (MTC)
• Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).

Pancreatitis (Severe Pancreas Inflammation)

Mounjaro may increase the risk of acute pancreatitis, a potentially life-threatening condition requiring immediate emergency care.

Emergency pancreatitis symptoms:

• Severe abdominal pain that won't subside
• Pain radiating from your abdomen to your back
• Nausea and vomiting with severe pain
• Fever and rapid pulse
• Abdominal tenderness.

Action required: Stop Mounjaro immediately and seek emergency medical care.

Hypoglycemia (Dangerous Low Blood Sugar)

Risk is higher when Mounjaro is combined with other diabetes medications like insulin, sulfonylureas (glipizide, glyburide, glimepiride), or other glucose-lowering drugs.

Low blood sugar warning signs:

• Dizziness, lightheadedness, confusion
• Sweating, shakiness, tremors
• Blurred vision, slurred speech
• Fast heartbeat, palpitations
• Anxiety, irritability, mood changes
• Hunger, weakness, fatigue
• Drowsiness, feeling jittery.

Serious Allergic Reactions (Anaphylaxis)

Stop Mounjaro and seek immediate emergency care for these anaphylaxis symptoms:

• Swelling of your face, lips, tongue, or throat
• Problems breathing or swallowing
• Severe rash or itching
• Fainting or feeling dizzy
• Very rapid heartbeat.

Kidney Problems and Dehydration

High-risk patients: Those with existing kidney disease, elderly patients, or those taking ACE inhibitors/diuretics.

Severe diarrhea and vomiting from Mounjaro can cause dangerous dehydration, leading to kidney damage.

Prevention strategies:

• Maintain adequate daily fluid intake
• Monitor urine output and color
• Report persistent vomiting or diarrhea immediately
• Contact a healthcare provider for signs of dehydration.

Gastroparesis (Delayed Stomach Emptying)

Mounjaro can cause severe, persistent stomach problems, including gastroparesis - abnormally slow gastric emptying.

Gastroparesis symptoms:

• Feeling full quickly when eating
• Persistent nausea and vomiting
• Abdominal bloating and pain
• Loss of appetite
• Weight loss (unintended).

Surgical and Anesthesia Risks

CRITICAL: Mounjaro slows gastric emptying, significantly increasing aspiration risk during surgery or procedures requiring anesthesia.

Required actions:

• Inform ALL healthcare providers about Mounjaro use before any procedures
• May need to stop medication before surgery (follow provider instructions)
• Anesthesiologists must be aware of delayed gastric emptying risks.

Gallbladder Problems

Gallbladder issues have occurred in some people who use Mounjaro. Tell your healthcare provider right away if you get symptoms of gallbladder problems, which may include:

• Pain in your upper stomach (abdomen)
• Fever
• Yellowing of skin or eyes (jaundice)
• Clay-colored stools.

NAION (Vision-Threatening Eye Condition)

Recent safety reports (emerging in 2024) have linked GLP-1 drugs like Mounjaro to non-arteritic anterior ischemic optic neuropathy (NAION), a rare vision-threatening condition.

Vision emergency symptoms to report immediately:

• Sudden vision changes or vision loss
• Vision loss in one or both eyes
• Blind spots in your visual field
• Difficulty seeing colors
• Eye pain or pressure

Additional eye risks: Diabetic retinopathy complications in patients with existing eye disease (known since original approval).

Talk to your healthcare provider if you have any side effect that bothers you or that does not go away. These are not all the possible side effects of Mounjaro. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Who Should Not Take Mounjaro?

Absolute Contraindications:

• Allergy to tirzepatide, Mounjaro, Zepbound, or any of the ingredients contained in the pens or vials (see below for a list of ingredients)
• Personal or family history of medullary thyroid carcinoma (MTC)
• Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).

Use with Caution:

• History of pancreatitis (severe abdominal pain)
• Severe kidney disease
• Gastroparesis or severe stomach problems
• History of gallbladder disease
• Diabetic retinopathy 
• Pregnancy or breastfeeding.

Pregnancy

Tell your healthcare provider if you are pregnant, you become pregnant, or plan to become pregnant while using this medicine. It is not known if this medicine will harm your unborn baby.

This medicine can make birth control pills less effective. Ask your doctor about other birth control options such as an injection, implant, skin patch, vaginal ring, condom, diaphragm, cervical cap, or contraceptive sponge. If you take birth control pills, you may need to use additional birth control methods for 4 weeks after starting this medicine, and for 4 weeks each time the dose is increased.

Breastfeeding

Tell your healthcare provider if you are breastfeeding or plan to breastfeed while using this medicine. It is not known whether this tirzepatide passes into your breast milk. Talk to your healthcare provider about the best way to feed your baby while using this medicine.

How should I use Mounjaro?

You should read the Instructions for Use carefully and ask your pharmacist or doctor to explain any part you do not understand. It is important to use this medicine exactly as directed. Do not take more or less of it or more often than your doctor prescribes.

Mounjaro is a pre-filled pen injected under the skin (subcutaneously).

• Mounjaro is usually given 1 time a week
• It can be given with or without meals at any time of the day
• It may be injected under the skin of the thigh, abdomen, or upper arm.
  • You should rotate the injection site for each dose.
  • See Where is the best place to inject Mounjaro? for more information.

Your healthcare provider will usually start you on a low dose, which will be gradually increased, but not more than once every 4 weeks.

You may change the day of the week you use this medicine as long as there are at least three days between doses.

You may give insulin in the same area as this medicine, but they should not be given right next to each other. Do not mix insulin and Mounjaro in the same injection.

Mounjaro controls type 2 diabetes but does not cure it. It may take four weeks or longer before you see the full benefit of this medicine. Continue to take this medicine even if you feel well. Do not stop taking this medicine without talking to your doctor.

For more detailed instructions with diagrams on how to use this medicine, click here: Instructions for Mounjaro.

Dosing Information

Dose of Mounjaro for Type 2 Diabetes (Adult):

• Initial dose: 2.5 mg SC once a week.
• After 4 weeks: Increase to 5 mg SC once a week.
• If additional glycemic control is needed: Increase from 5 mg to 7.5 mg for 4 weeks and thereafter in 2.5 mg increments after at least 4 weeks on the current dose.
• Maximum dose: 15 mg subcutaneously once a week.

Comments: The 2.5 mg dosage is for starting treatment and is not intended for glycemic control.

The day of weekly administration can be changed, if necessary, as long as the time between the 2 doses is at least 3 days (72 hours).

What strengths are Mounjaro pens?

Mounjaro is available as a single-dose autoinjector pen or vial in the following strengths:

• 2.5 mg/0.5 mL 
• 5 mg/0.5 mL 
• 7.5 mg/0.5 mL 
• 10 mg/0.5 mL 
• 12.5 mg/0.5 mL 
• 15 mg/0.5 mL.

In the past, there have been issues with Mounjaro availability due to increased demand, leading to drug shortages for some strengths. This is now resolved.

What should I do if I miss a dose?

Take the missed dose as soon as you remember it within 4 days after the missed dose.

However, if more than 4 days have passed, skip the missed dose and continue your regular dosing schedule. Do not inject two doses within 3 days of each other.

What should I do in case of an overdose?

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at Poison Help If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

What other drugs affect Mounjaro?

Tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.

Birth control pills may not work as well while receiving Mounjaro (see birth control interaction warning below). Your doctor may suggest you use another form of birth control for 4 weeks after starting this medicine and for 4 weeks after each dose change.

Taking other medicines to treat diabetes, like insulin, sulfonylureas, or other GLP-1 agonists such as Ozempic (see Mounjaro vs Ozempic) with this treatment may increase your risk of low blood sugar levels. Talk to your doctor and pharmacist about low blood sugar and how to manage it.

This medicine delays gastric emptying and has the potential to change the absorption of other medicines that are taken orally.

This list is not complete. Many other drugs may interact with this medicine, including prescription and over-the-counter medicines, vitamins, and herbal products. To check for interactions with this medicine click the link below.

Birth Control Interaction Warning: Oral Contraceptive Effectiveness Reduced

IMPORTANT: Mounjaro may reduce the effectiveness of oral birth control pills due to delayed gastric emptying. This interaction has been known since the original FDA approval, but recent studies have quantified the extent:

• Approximately 20% decrease in overall exposure of oral contraceptives after a single 5 mg dose of Mounjaro.

Contraceptive recommendations:

• Switch to non-oral contraceptive methods (IUD, implant, injection, patch)
• Add barrier methods (condoms, diaphragm)
• Use alternative birth control for 4 weeks after starting and after each dose increase.

How do I store Mounjaro?

Store your Mounjaro pens in the refrigerator between 36⁰F to 46⁰F (2⁰C to 8⁰C) in their original carton to protect them from light.

If needed, or while traveling, each single-dose Mounjaro pen can be stored at room temperature up to 86⁰F (30⁰C) for up to 21 days.

Ingredients

Active ingredient: tirzepatide

Inactive ingredients: sodium chloride, sodium phosphate dibasic heptahydrate, and water for injection. Hydrochloric acid solution and/or sodium hydroxide solution may have been added to adjust the pH.

Manufacturer

Mounjaro is made by Eli Lilly and Company, commonly known as Lilly. They are an American pharmaceutical company based in Indianapolis that was founded in 1876. 

Frequently Asked Questions About Mounjaro Side Effects

How long do Mounjaro side effects last?

Most common side effects (nausea, diarrhea) typically improve within 4-8 weeks as your body adjusts to the medication.

Can I prevent Mounjaro side effects?

While not entirely preventable, taking with food, starting with lower doses, and following dietary recommendations can minimize side effects.

How can I manage common Mounjaro side effects?

For nausea and vomiting:

• Eat smaller, more frequent meals
• Avoid fatty, greasy, or spicy foods
• Stay hydrated with clear fluids
• Consider ginger supplements (consult your doctor first).

For diarrhea:

• Stay well-hydrated with electrolyte solutions
• Follow the BRAT diet (bananas, rice, applesauce, toast)
• Avoid dairy products temporarily
• Monitor for signs of dehydration.

For decreased appetite:

• Focus on nutrient-dense foods
• Eat smaller portions more frequently
• Monitor weight loss (report excessive loss to your doctor)
• Consider protein supplements if needed.

Are Mounjaro side effects dangerous?

Most side effects are mild and temporary. However, serious side effects like pancreatitis and thyroid tumors require immediate medical attention.

Should I stop Mounjaro if I have side effects?

Don't stop without consulting your doctor. Many side effects improve with time or dose adjustments.

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