Mounjaro Pen Malfunction: Your Dose, Reporting and Replacement Fills

If your Mounjaro pen failed during an injection, or you can't tell whether the dose went in, don't start a second injection on your own. If you already did and think you may have taken too much, call your healthcare provider or Poison Help at 1-800-222-1222, or go to the nearest emergency room.¹

Do this now:

1. Single-dose pen, no gray plunger showing? Call Lilly at 1-800-LillyRx (1-800-545-5979), 9 a.m. to 5 p.m. ET, Monday through Friday.² Until you reach them, store the pen safely so no one is stuck by the needle.¹
2. KwikPen, no 0 in the dose window after you pull the needle out? Put the needle back into your skin and finish the injection, without dialing again. If you still think you didn't get the full dose, don't start over or repeat the injection.¹
3. Before your next injection, ask your prescriber or pharmacist how to handle this week's dose.
4. Keep the pen and its carton, and report the problem through Lilly's product help tool, because Lilly and FDA both ask for details printed on the package.^{2, 3, 4}
5. Ask your pharmacy about a replacement fill, or your plan about an early refill. Lilly's reporting pages don't say whether Lilly replaces a pen.^{2, 3}

Start with which pen you have. Six steps follow: check the pen and your dose (symptoms that need help first are at the top of that step), report it to Lilly, ask about a replacement fill, report it to FDA, make sure the pen is genuine and get rid of it safely. Mounjaro's label warnings come last.

Which Mounjaro pen do you have?

Mounjaro is Lilly's brand of tirzepatide. Its US label lists two kinds of pen, and their steps differ, so match yours first. (Mounjaro also comes in vials, which this page doesn't cover.)¹

These are the US instructions. If you live outside the US, follow the leaflet in your box and your country's reporting route. If your tirzepatide is compounded (made by a compounding pharmacy, as many telehealth companies sell it), Lilly's steps won't cover it: see the compounded section in Step 5. A genuine Lilly pen prescribed through a telehealth service is covered by the steps on this page.

Single-dose pen. A carton holds 4 pens, each used for one weekly injection. You pull off the gray base cap, place the clear base on your skin, turn the lock ring, then press and hold the purple button for up to 10 seconds. The first click means the injection has started, the second that it has finished, and the gray plunger then shows. This pen has no priming or dose-setting step.¹

KwikPen. One pen holds 4 fixed weekly doses. Each week you attach a new pen needle (not included with the pen), prime the pen to remove air and check that it works, then turn the dose knob until it stops and a 1 shows in the dose window. After 4 doses the pen won't let you dial a full dose, and you throw it away with the leftover medicine.¹

Never share a KwikPen or its needles, even if you change the needle. The label says sharing can give someone else a serious infection, or give you one.¹

Who should inject. Both pens' instructions say people with vision problems should not use the pen without help from a person trained to use it, so if that's you, have your helper do the checks below. The Medication Guide adds that children should not inject themselves with the KwikPen: an adult caregiver should give a child's injections.¹

Step 1: Check the pen and your dose

Deal with symptoms first. Reporting the pen can wait.

Get help right away if:

• You think you took too much Mounjaro. Call your healthcare provider or Poison Help at 1-800-222-1222, or go to the nearest emergency room.
• You have severe stomach pain that won't go away, with or without nausea or vomiting. It may spread to your back. Stop using Mounjaro and call your healthcare provider: this can be pancreatitis (an inflamed pancreas), which has been fatal in some people taking Mounjaro or similar medicines.
• You have signs of a serious allergic reaction: swelling of your face, lips, tongue or throat; problems breathing or swallowing; severe rash or itching; fainting or feeling dizzy; or a very rapid heartbeat. Stop using Mounjaro and get medical help.
• Nausea, vomiting or diarrhea won't go away. Tell your healthcare provider and keep drinking fluids. Losing fluids can lead to kidney problems, in some cases serious enough to need dialysis.
• You have signs of a gallbladder problem: pain in your upper stomach, fever, yellow skin or eyes, or clay-colored stools. Tell your healthcare provider.¹

Low blood sugar. If you also use insulin or a sulfonylurea (a type of diabetes pill), your risk of low blood sugar, including severe low blood sugar, may be higher. Signs can include dizziness, sweating, shakiness, confusion, headache, a fast heartbeat and hunger. If you have these signs now, treat them the way your care team showed you, and let them know. The Medication Guide asks you to talk with your provider about how to manage low blood sugar, so do that if you haven't yet.¹

Very low blood sugar can cause loss of consciousness or a seizure and needs treatment right away. Tell the people around you to call 911 right away after they give you glucagon, or if you don't have a glucagon kit with you.⁵

Then follow the part for your pen. Neither pen's instructions describe a reset button or any other way to reset the pen.¹ The KwikPen's instructions say not to move medicine from the pen into a syringe, and the UK's medicines regulator advises never trying to extract doses from a defective pen.^{1, 6}

If you use the single-dose pen

Normal, not a defect: air bubbles in the pen; a drop of liquid on the needle tip when the gray base cap comes off; a soft click just before the second loud click; and a drop of liquid or blood on your skin afterward. Keep the pen against your skin until you hear the second loud click. You don't need to warm the pen to room temperature first.¹

Don't inject with the pen if:

• the label shows the wrong medicine or dose, or the pen has expired;
• the pen looks damaged;
• the medicine is frozen or cloudy, has particles, or isn't colorless to slightly yellow;
• the pen was ever frozen, or has been at room temperature (up to 86°F, or 30°C) for more than 21 days in total;
• it got hotter than 86°F (30°C), for example in a hot car, which is past the label's room-temperature limit. Ask your pharmacist or Lilly before you use it;
• you dropped it on a hard surface, since it has glass parts;
• you pressed the purple button before pulling off the gray base cap. Leave the cap on.¹

For several of these, the instructions say to throw the pen away and use a new one.¹ If you'll report a problem with the pen itself, keep it, but don't use it. Step 2 says how to store it.

Did the dose go in? Your dose was delivered if the gray plunger is visible. If you don't see the plunger, the instructions say to call Lilly at 1-800-LillyRx (1-800-545-5979) for further instructions, and to store the pen safely until then to avoid an accidental needle stick. For other problems with the pen, they say to call Lilly or your healthcare provider.¹

If you use the KwikPen

Normal, not a defect: a drop of medicine on the needle tip after the injection, which the instructions say will not affect your dose, and medicine left in the pen after 4 doses. Don't inject that leftover medicine.¹ Our pen and vial guide explains why some liquid stays in a pen and why that is no reason for another dose.

Don't inject with the pen if:

• the medicine name or strength doesn't match your prescription;
• the pen has expired (EXP) or looks damaged;
• the medicine has been frozen, has particles, is cloudy or is discolored;
• 30 days have passed since your first dose from it, or you have taken 4 doses;
• it has been at room temperature (up to 86°F, or 30°C) for more than 30 days in total, opened or not;
• it got hotter than 86°F (30°C), for example in a hot car, which is past the label's room-temperature limit. Ask your pharmacist or Lilly before you use it.¹

If priming shows no medicine, repeat the priming steps no more than 2 more times. If there is still no drop, change the pen needle and try no more than 1 more time. If there is still nothing, call Lilly at 1-800-LillyRx (1-800-545-5979).¹

Other troubleshooting steps in the instructions:

• Cap stuck: twist it gently back and forth, then pull it straight off.
• Dose knob hard to push: push more slowly. Your needle may be blocked, so put on a new pen needle and prime again. If dust, food or liquid may have gotten inside the pen, throw it away and use a new pen.
• Dose knob won't turn far enough for the 1 to show in the dose window: throw the pen away with the medicine left in it. There may not be enough for a full dose, so don't try to inject it.¹

The instructions don't cover a dose knob that comes off. That fault turned up in the falsified pens the UK regulator found, so see Step 5.

For several of the steps above, the instructions say to throw the pen away. If you'll report a problem with the pen itself, keep it, but don't use it. Step 2 says how to store it.

Did the dose go in? Push the dose knob in until it stops, then slowly count to 5 while you hold it. A 0 must show in the dose window before you pull the needle out.¹

After you pull the needle out, check the window again. If you see the 0, you got the full dose. If you don't, put the needle back into your skin and finish the injection, without dialing again. If you still think you didn't get the full dose, the instructions say not to start over or repeat the injection.¹

A missed dose, or one that may not have gone in fully

Mounjaro's label gives this rule for a missed dose: take it as soon as possible within 4 days (96 hours) of when it was due. If more than 4 days have passed, skip it and take the next dose on your usual day. Never take 2 doses within 3 days of each other.¹

That rule is written for a dose you didn't take. The label's rule covers one missed dose and says nothing about restarting after a longer break. For an injection that may have gone in only partly, the instructions give only the "Did the dose go in?" steps above.¹

Before you inject again, ask your prescriber or pharmacist how to handle this week's dose and when to take the next one. If you won't have a working pen before your next dose is due, tell your prescriber.

If you have diabetes, keep checking your blood sugar the way your care team told you to, and call them if your readings run higher or lower than the range they gave you. Before you use another pen or buy another fill, Mounjaro's label warnings are worth going over with your prescriber.

Step 2: Report the pen to Lilly

As of October 4, 2026, Lilly's report page splits reports from the US into two groups:²

• A product concern (quality, usability or appearance, or replacement support): use Lilly's product help and support tool, which is meant for US patients 18 or older reporting for themselves.^{2, 3}
• Everything else, including a side effect (with or without a pen problem), a report for someone else, or an anonymous report: call Lilly Support Services at 1-800-LillyRx (1-800-545-5979), 9 a.m. to 5 p.m. ET, Monday through Friday.² Both pens' instructions give this number for pen problems.¹ The product help tool also sends side effects and reports on someone else's behalf to an online Lilly Safety Reporting Tool.³

Have this ready. Lilly asks for:^{2, 3}

• your contact details, which the tool says should match what your pharmacy has on file, and your age;
• the product name and dose;
• the batch or lot number, and other details from the package;
• the date of the problem and a description of what happened.

Photos of all sides of the pen and carton help too: FDA says they help it review a report, and its form asks whether you have a picture.⁴ You can also ask Lilly whether the other pens from the same carton are safe to use.

Keep the pen, but don't use it. For a quality problem, Lilly asks you to keep the device for 21 days if you still have it.² Store it apart from your other pens, mark it so no one injects with it by mistake, and keep it out of children's reach, where no one can be stuck by the needle.

For a KwikPen, the instructions say to carefully put the outer needle shield back on, unscrew the capped needle into a sharps container and put the pen cap back on before you store it.¹ If someone other than you is stuck by the used needle, FDA says to wash the spot right away with soap and water or a skin disinfectant such as rubbing alcohol or hand sanitizer, then call a physician or the local hospital right away.⁷

What happens next. You get a confirmation after an online report, and Lilly says it contacts you only if it needs more information. For quality problems, a Lilly representative may contact you within 3 to 5 business days, through the channel you chose in the tool. Lilly asks you not to call to follow up, saying it won't speed things up. A new problem needs a new report.²

What Lilly's reporting pages don't say. They list "product replacement support" as a topic, but they don't say whether Lilly replaces a pen, how, or how long it takes, and they don't mention vouchers or refunds. The 3 to 5 business days refers to a possible call, not a replacement.^{2, 3} That is why Step 3 covers your pharmacy or plan at the same time.

Zepbound pens. The same reporting routes apply to Zepbound, Lilly's other tirzepatide medicine.² Its pen instructions match on the key points: no gray plunger means call Lilly at the same number, don't repeat a KwikPen injection, and never share a KwikPen.⁸ Its warnings are in its own label and Medication Guide, and they differ from Mounjaro's in places. For example, Zepbound's label says to stop it when a pregnancy is recognized.⁸

Outside the United States. Lilly asks you to use your country's Lilly site, through the globe icon at the top of its report page, and to follow your country's reporting rules.² In the UK, the medicines regulator (the MHRA) asks for suspected defective pens to be reported to its Yellow Card scheme.⁶

Step 3: Ask your pharmacy or plan about replacement fills

If the problem came from shipping or handling. For medicine that arrived warm, in a damaged container, or not at all, Lilly's tool sends you to the pharmacy that dispensed it. If you paid cash and your order came from Gifthealth, one of the dispensing pharmacies LillyDirect works with, the tool points you to Gifthealth's help center for LillyDirect orders instead.^{3, 9}

That help center has a section for Mounjaro. It says it's normal for medicine to feel slightly warm or cold on arrival, and that if you're concerned about the temperature you should contact its patient care team for a temperature assessment. Its help articles also list a phone number, (833) 707-6619, and a chat option.¹⁰

FDA advises against using any injectable GLP-1 medicine that arrives warm or without enough refrigeration.¹¹ Mounjaro's label does allow limited time at room temperature, within the limits given in Step 1.¹ If you're not sure a delivery stayed cold enough, ask the dispensing pharmacy before you use it.³

If insurance paid for your pens. Ask the pharmacist whether your plan allows an early refill to replace a damaged pen. For example, Centene's policy for its Medicaid plans, revised November 14, 2025, allows an early refill for lost, spilled, broken or damaged medicine. The dispensing pharmacist contacts the plan's pharmacy services, and if the plan agrees, the member gets the rest of the missing fill, limited to once a year.¹² Your plan's rules may differ.

If you pay cash. Report the pen through Lilly's tool, and take a shipping problem to the dispensing pharmacy or Gifthealth's help center, as above. Lilly's reporting pages don't say whether a self-pay replacement costs anything.^{2, 3}

As of October 4, 2026, LillyDirect, Lilly's direct-to-patient service, lists self-pay Mounjaro single-dose pens from $499 for a fill of 4 pens, which it calls a month's supply, at every strength, plus any taxes and fees.^{9, 13} The offer is for buyers 18 or older in the US or Puerto Rico who have a prescription for an approved use.¹³ For help with refills, call LillyDirect at 1-844-559-3471.⁹

Mounjaro is approved for type 2 diabetes, not for weight loss, so using it for weight loss alone is off-label (outside its FDA-approved uses) and doesn't meet LillyDirect's approved-use condition.^{1, 13} If that is your situation, talk with your prescriber. Zepbound, Lilly's other tirzepatide medicine, is FDA-approved, used with a reduced-calorie diet and more physical activity, to help adults with obesity, or with overweight and at least one weight-related condition, lose excess weight and keep it off.⁸ Our page on LillyDirect's Mounjaro prices has more.

Step 4: Report it to FDA's MedWatch program

MedWatch takes voluntary reports from patients and consumers as well as health professionals. FDA asks for reports of product quality problems, such as a product that isn't working properly or has a defect, and lists auto-injectors and prefilled syringes among the products you can report.¹⁴

• Online: use the MedWatch Online Voluntary Reporting Form and choose the consumer and patient version (Form 3500B). You have 3 days to finish once you start. You can't edit a report after you submit it, but you can file a new one with more information.¹⁴
• On paper: download Form 3500B and mail or fax it. The form lists the address and a toll-free fax number.⁴
• By phone, for side effects: the Mounjaro label gives FDA's line, 1-800-FDA-1088.¹

What the form asks for: the product name as it appears on the box, where and when you bought it, the company that makes it, the expiration date, lot number, NDC (National Drug Code) number and strength, and whether you still have the product and a picture of it. Fill in what you can, even without every detail. Someone else can fill in the form for you.⁴

After you file: keep the pen in case FDA contacts you, and don't send it to FDA. The form gives no time limit for keeping it. FDA replies once it gets your report and contacts you again only if it needs more information.⁴

Your report goes into a database, where an FDA safety evaluator reviews it and compares it with other reports. The form doesn't say that FDA will replace a product or settle a complaint. FDA may share your name and contact details with the manufacturer unless you check the box asking it not to.⁴

Step 5: Check that the pen is genuine

A faulty pen can be a sign of a fake. In February 2026, the MHRA reported falsified Mounjaro KwikPen 15 mg pens supplied through one UK online pharmacy. They were found because the pens were faulty: in all but one case, the dose knob came off during use.⁶

In the US, FDA has reported seizing counterfeit Ozempic pens (a semaglutide medicine made by Novo Nordisk) from the drug supply chain more than once, most recently in an update dated December 5, 2025.¹⁵ In an earlier update, dated December 21, 2023, FDA said analysis of samples of the seized pens found counterfeit needles, so the needles' sterility could not be confirmed, which it said raises the risk of infection.¹⁵ Lilly says fakes are often advertised and sold online, through social media or at certain med spas.¹⁶

Check yours. Lilly's medicine verification web app covers Mounjaro and Zepbound obtained in the US. Scan the 2D barcode on the outside of the package with your phone. It checks whether the serial number is consistent with medicine made by Lilly and obtained in the US. Don't scan the pen itself.¹⁷

If you think your pen is fake, don't use it. Lilly says counterfeit or fake products are never safe to use, and asks anyone who may have received or used one to contact their health care provider or seek immediate medical attention.¹⁶ In the UK case, the MHRA told people who had injected from an affected pen and had unusual symptoms they were concerned about to seek immediate medical attention.⁶

Lilly also asks you to call 1-800-LillyRx (1-800-545-5979), which its counterfeit page calls the Lilly Answers Center, and to report the product to local law enforcement, your state Board of Pharmacy or your state poison control center.¹⁶

FDA's counterfeit Ozempic notice says suspected counterfeit products may be reported to its consumer complaint coordinator or through its suspected-criminal-activity form, and asks consumers to report side effects to MedWatch.¹⁵ FDA also encourages patients to report quality problems with any medicine to MedWatch.¹¹

Where to buy. FDA urges people buying GLP-1 drugs online to buy only from state-licensed pharmacies.¹¹ Its counterfeit Ozempic notice adds that patients should get Ozempic only with a valid prescription through state-licensed pharmacies and check the product before using it for any signs of counterfeiting.¹⁵ Lilly names its LillyDirect service as one way to get genuine Lilly medicine with a valid prescription.¹⁶

If your medicine is compounded tirzepatide (prepared by a compounding pharmacy or an outsourcing facility), Lilly's product help tool and barcode check won't cover it, because they are for Lilly's own products.^{3, 4, 17} Compounded drugs are not FDA-approved, and FDA does not review them for safety, effectiveness or quality before they are marketed.¹¹ For questions about a compounded drug's instructions or label, FDA says to contact the compounder that made it or the telehealth platform where you bought it.¹¹

Compounded drugs come with no FDA-approved Medication Guide or Instructions for Use, so the warning signs in Step 1 are what Mounjaro's Medication Guide says, not guidance written for your product. Ask your prescriber how to handle a dose that may not have gone in, go over those signs and the label warnings below with them, and get help the same way if you have any of the signs.

To report a problem, use MedWatch: its consumer form has a box for compounded products.⁴ FDA says side effects from compounded semaglutide and tirzepatide are likely underreported, and that many of those reported look like the side effects of the FDA-approved drugs.¹¹ Our pages on checking a compounded tirzepatide provider and on dose mix-ups with compounded pens and vials cover more.

Step 6: Dispose of the pen safely

If you reported a quality problem to Lilly, keep the pen until the 21 days it asks for have passed.² If you also reported it to FDA, keep it longer: the form asks you to keep the product in case FDA contacts you and sets no end date.⁴ Then follow the instructions for your pen:¹

• Single-dose pen: put the whole pen in an FDA-cleared sharps disposal container. Never put it in household trash.
• KwikPen: put used pen needles in a sharps container right away. With the needle off, the pen itself can go in household trash or a sharps container.

For household sharps containers and what to do when one is full, see the sharps section of our pen and vial guide.

Before you inject again: Mounjaro's label warnings

These are the label warnings to go over with your prescriber before you use another pen or buy another fill. They are not all of its warnings: Mounjaro's label and Medication Guide list the rest.¹

Thyroid tumors. The boxed warning says tirzepatide caused thyroid tumors in rats. Whether Mounjaro causes them in people, including a thyroid cancer called medullary thyroid carcinoma (MTC), is unknown. Tell your healthcare provider if you get a lump or swelling in your neck, hoarseness, trouble swallowing or shortness of breath, which may be symptoms of thyroid cancer.¹

Who must not use it. The label rules Mounjaro out for people with a personal or family history of MTC, for people with multiple endocrine neoplasia syndrome type 2 (MEN 2), an endocrine system condition, and for anyone who has had a serious allergic reaction to tirzepatide or any other ingredient in Mounjaro. It does not recommend Mounjaro for people with severe gastroparesis (a stomach that empties very slowly).¹

Pregnancy and breastfeeding. If you are pregnant, plan to become pregnant or are breastfeeding, tell your prescriber. Based on animal studies, Mounjaro may cause harm to an unborn baby, and poorly controlled diabetes in pregnancy carries risks too, so the label says to use Mounjaro in pregnancy only if the possible benefit justifies the possible risk. That is a decision to make with your prescriber, not on your own. Mounjaro may pass into breast milk, so talk with your provider about the best way to feed your baby.¹

Birth control pills. Mounjaro may make birth control pills work less well, an effect that is largest after the first dose. The label advises a non-pill method, or an added barrier method, for 4 weeks after you start Mounjaro and for 4 weeks after each dose increase.¹

Other pills and surgery. Mounjaro slows stomach emptying, which can affect how some pills are absorbed, and the label names warfarin as one to monitor. Slow stomach emptying may also lead to complications with anesthesia or deep sedation, so tell all your healthcare providers that you use Mounjaro before any planned surgery or procedure.¹

Your eyes. If you have a history of diabetic retinopathy (diabetic eye disease), your provider should monitor it, because it has temporarily worsened with rapid improvement in blood sugar control. Tell your provider about any changes in your vision.¹

Stomach problems. Besides the severe stomach pain listed under "Get help right away," tell your healthcare provider about any stomach problems that are severe or won't go away.¹

Sources

1. MOUNJARO (tirzepatide) injection and KwikPen: prescribing information, Medication Guide and Instructions for Use (updated August 27, 2026), Eli Lilly and Company, via DailyMed, National Library of Medicine, accessed October 4, 2026.
2. How to Report a Lilly Product Concern, Eli Lilly and Company, accessed October 4, 2026.
3. Product help & support, Eli Lilly and Company, accessed October 4, 2026.
4. MedWatch Consumer Voluntary Reporting, Form FDA 3500B (09/2025), U.S. Food and Drug Administration, accessed October 4, 2026.
5. Low Blood Glucose (Hypoglycemia) (last reviewed July 2021), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, accessed October 4, 2026.
6. Falsified Mounjaro KwikPen 15mg pre-filled pens (Drug Safety Update, published February 24, 2026), Medicines and Healthcare products Regulatory Agency, GOV.UK, accessed October 4, 2026.
7. Safely Using Sharps (Needles and Syringes) at Home, at Work and on Travel (content current as of November 19, 2021), U.S. Food and Drug Administration, accessed October 4, 2026.
8. ZEPBOUND (tirzepatide) injection and KwikPen: prescribing information, Medication Guide and Instructions for Use (updated August 28, 2026), Eli Lilly and Company, via DailyMed, National Library of Medicine, accessed October 4, 2026.
9. Authentic Mounjaro (tirzepatide) Shipped to You | LillyDirect, Eli Lilly and Company, accessed October 4, 2026.
10. LillyDirect Powered by Gifthealth (help center), including its articles What should I do if I am concerned by the temperature of my medication when it arrives? and Can I return my medication?, Gifthealth, accessed October 4, 2026.
11. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss (content current as of October 1, 2026), U.S. Food and Drug Administration, accessed October 4, 2026.
12. Lost, Stolen, Spilled, or Broken Medication, policy CC.PHARM.CS.05 (Medicaid; revised November 14, 2025), Centene Corporation, posted by Oklahoma Complete Health, accessed October 3, 2026.
13. Mounjaro (tirzepatide): LillyDirect Pharmacy Self Pay Purchase Offer Terms, Eli Lilly and Company, accessed October 4, 2026.
14. MedWatch Online Voluntary Reporting Form, U.S. Food and Drug Administration, accessed October 4, 2026.
15. FDA warns consumers not to use counterfeit Ozempic (semaglutide) found in U.S. drug supply chain (content current as of December 5, 2025), U.S. Food and Drug Administration, accessed October 4, 2026.
16. Identify Real Lilly Medicine, Eli Lilly and Company, accessed October 4, 2026.
17. Identifying your Zepbound (tirzepatide) and Mounjaro (tirzepatide) medication, Eli Lilly and Company, accessed October 4, 2026.

How we made this page

A pen that may have failed raises urgent questions: did the dose go in, and what do I do now? The older PlexusDx post at this address, like several other pages on the subject, answered some of them with steps or promises that Lilly's instructions don't support. This page replaces it.

AI tools drafted it from the sources listed above. The two US leaflets differ (the single-dose pen's was revised in April 2026, the KwikPen's in January 2026), so each check, fix and stop point was kept with its own pen. The dose rule, warning signs and label warnings come from Mounjaro's Medication Guide and prescribing information on DailyMed (updated August 27, 2026), and the low-blood-sugar advice from NIDDK. Lilly's reporting process comes from its product-concern, product-help, counterfeit and LillyDirect pages; Gifthealth's from its help center; FDA's from the MedWatch form, Form 3500B and its pages on unapproved GLP-1 drugs, counterfeit Ozempic and sharps; the UK case from the MHRA's notice.

On October 4, 2026, AI tools matched the passage behind each instruction to the current US leaflet for that pen, and each Lilly, FDA, Gifthealth, MHRA and NIDDK step to the page it cites, as that page read that day. AI reviews of the draft then flagged errors, which were fixed before this version. Matching words to sources can't tell you whether your pen is safe to use. Lilly, your pharmacist and your prescriber can.

We also set the US leaflets against five other pages on Mounjaro pen problems, from two telehealth companies and three UK online pharmacies or health services. Some gave steps the leaflets don't include, such as warming the pen, using a dropped pen after a look, or resetting the dial, and some described free replacements or vouchers that Lilly's pages don't mention. We used none of it, and no one handled a pen for this page.

The older PlexusDx post at this address gave a phone number that is not on the Lilly pages we checked, a malfunction rate it gave no source for, replacement timelines Lilly doesn't state and a pitch for compounded medicine; none of its text was kept.

Jay Hastings reviewed and approved this version on October 19, 2026. Dr. Asad K. Niazi, MD, MPH, reviewed the medical content on October 17, 2026. He is co-founder and CEO of Lone Star Virtual Health, the company that provides PlexusDx's prescribing clinicians, so he has a business relationship with PlexusDx. PlexusDx sells compounded GLP-1 treatment, so we have a financial interest in this topic. See our editorial policy.