Mounjaro comes in a single-dose pen that’s designed to be simple: you uncap it, place it on your skin, and press and hold a button. The whole injection takes about 10 seconds. But the first time you do it, the process can feel intimidating, so here’s exactly what to expect from start to finish.
Before You Inject
Check the pen before each use. Look at the base cap area and confirm the red inner seal is intact. If it’s damaged, don’t use that pen. Also check the expiration date and the liquid itself through the viewing window. The medication should be clear and colorless to slightly yellow. If it looks cloudy or has particles floating in it, use a different pen.
If your pen has been in the refrigerator, let it sit at room temperature for about 20 to 30 minutes before injecting. Cold medication stings more going in. Don’t try to speed this up with a microwave or warm water.
Wash your hands thoroughly, and clean the injection site with an alcohol swab if desired.
Choosing Where to Inject
You have three options for injection sites:
- Stomach (abdomen): At least 2 inches away from your belly button.
- Front of the thigh: Midway between the hip and the knee.
- Back or outer part of the upper arm: This one works best if a caregiver is giving you the shot, since it’s hard to reach on your own.
Rotate your injection site each week. Don’t inject in the exact same spot two weeks in a row, as repeated injections in one area can cause lumps under the skin (called lipohypertrophy). A practical approach is to pick the same general area, like your abdomen, but shift to a different spot within that area each time, rotating between quadrants.
Step-by-Step Injection Process
Pull off the gray base cap. You’ll see the needle is already attached inside the pen, but it’s hidden. You won’t see it before, during, or after the injection.
Place the flat base of the pen firmly against your skin at your chosen site. You want the pen perpendicular to your body, pressed flush against the skin. Then unlock the pen by turning the clear lock ring.
Press and hold the purple injection button. You’ll hear a loud click, which means the injection has started. Keep holding the pen against your skin. A second click will follow, and you’ll see a gray plunger appear in the viewing window. After the second click, slowly count to 10 while keeping the pen in place. This ensures the full dose is delivered.
Pull the pen straight away from your skin. The needle retracts automatically, so you won’t see it. The purple button will be locked in its pressed position, confirming the dose was given.
What to Do If You Miss a Dose
Mounjaro is a once-weekly injection, and you can take it on any day of the week. If you forget your scheduled dose, you have a 4-day (96-hour) window to take it late. If more than 4 days have passed since you missed it, skip that dose entirely and take the next one on your regular day. Never take two doses within 3 days of each other.
If you want to change your injection day, that’s fine as long as at least 3 days have passed since your last dose.
The Dosing Schedule
Everyone starts at 2.5 mg once weekly. This starting dose is designed to let your body adjust to the medication, not to provide the full therapeutic effect. After 4 weeks at 2.5 mg, your dose increases to 5 mg. From there, your prescriber may continue increasing the dose in 2.5 mg increments every 4 weeks or longer, depending on how you’re responding and tolerating side effects. The gradual ramp-up reduces the chance of nausea and other gastrointestinal issues.
Each dose level has its own color-coded pen, so you’ll get new pens from the pharmacy as your dose changes.
Tips for Reducing Pain
Most people describe the Mounjaro pen injection as a quick pinch, but if you’re sensitive to needles or finding it uncomfortable, a few strategies help. Letting the pen reach room temperature before injecting is the single most effective step. Beyond that, applying an ice pack to the site for about 15 minutes beforehand numbs the skin. You can also try sitting down instead of standing, which relaxes the muscles at the injection site.
Tension makes injections hurt more. If you’re anxious, distract yourself with music, a phone call, or a show. After the injection, gently massaging the area can help disperse the medication and reduce soreness.
Storage Guidelines
Keep unused Mounjaro pens in the refrigerator between 36°F and 46°F (2°C to 8°C). If you need to travel or prefer to keep a pen out, unused pens can be stored at room temperature (up to 86°F or 30°C) for up to 30 days. After 30 days out of the fridge, an unused pen should be discarded. Never freeze Mounjaro, and don’t use a pen that’s been frozen.
Once you’ve used a pen, it goes straight into a sharps container. Don’t save it or try to get a second dose out of it. Each pen contains exactly one dose.
Disposing of Used Pens
Place the used pen into a sharps disposal container immediately after injection. If you don’t have one, you can purchase FDA-cleared sharps containers at most pharmacies, or use a heavy-duty plastic household container with a tight-fitting lid (like a laundry detergent bottle) as a temporary substitute. Fill the container no more than three-quarters full.
When your container is ready for disposal, options vary by location. Many pharmacies, hospitals, and fire stations serve as drop-off sites. Some communities offer mail-back programs or special waste pickup services. Check with your local health department or trash removal service for the specific options near you.
Troubleshooting a Pen That Won’t Work
If the button is hard to press or the pen seems jammed, don’t force it. The most common causes are a blocked needle, dust or liquid contamination inside the pen, or pressing the button too quickly. If the pen doesn’t fire properly, discard it and use a new one. Check that the red inner seal was intact before use, as a broken seal means the pen was compromised.
If you’re unsure whether you received the full dose, look at the viewing window. The gray plunger should be visible. If it’s not, or if the purple button didn’t lock into place, the dose may not have been delivered completely. Don’t attempt to reuse the pen. Contact Lilly’s customer line at 1-888-545-5972 for a replacement if you suspect a defective pen.