To store Mounjaro, keep the pen in the fridge between 2C and 8C before first use, out of the freezer and away from direct heat and light. Once in use, many pens can be kept below 30C for a limited number of days, as set out in the product information. Using it is straightforward too: choose a weekly day, inject into the fatty tissue of the stomach, thigh or upper arm, and follow your pen's instructions.
Most people find the weekly injection quick and near-painless once they have done it a couple of times. This guide covers the practical basics: choosing a day, where and how to inject, how to store your pen, and what to do if you miss a dose. Getting the routine right matters, because good storage and technique keep the medicine effective and the process comfortable.
How to store Mounjaro and other GLP-1 pens
Storage matters for these medicines. Before first use they generally need refrigeration between 2C and 8C; many pens can then be kept at room temperature, usually below 30C, for a limited period once in use. Do not freeze them, and keep them out of direct heat and sunlight. The Mounjaro product information and the Wegovy product information give the exact temperatures and in-use time limits, so check yours rather than guessing. If a pen has frozen, do not use it.
Choosing your day and time
Weekly injections can be taken on any day, with or without food, but keeping to the same day each week builds a reliable habit. Many people pick a quieter day. You can change the day if needed, within the guidance in your product information, but consistency helps you remember. Our guide to the first 12 weeks on treatment covers how this fits the wider routine.
Is Mounjaro a GLP-1, and where do you inject it?
Mounjaro (tirzepatide) acts on the GLP-1 receptor and a second gut hormone receptor, so it works on the same appetite pathways as other GLP-1 weight loss treatments. Not all GLP-1 treatments are injections; there is an oral form too, as our guide to oral versus injectable GLP-1 explains. For the injectable pens, the usual sites are the abdomen (avoiding the area right around the navel), the front of the thighs, or the back of the upper arms. Rotating between sites, and varying the exact spot, helps keep the skin comfortable. The needle is very fine and short, and injects into the fatty layer just under the skin.
How to inject step by step
Pens vary, so the leaflet for your specific pen is the authority. In general: check the pen and the medicine, attach a new needle if required, choose and clean the site, then follow the pen's steps to deliver the dose, holding for the stated time. Dispose of needles in a sharps bin, never in household waste. If you are new to injecting, our step-by-step guide to how to inject Mounjaro walks through the technique.
A few practical points make it smoother. Let a refrigerated pen sit for a short while so it is not fridge-cold, which can sting less. Clean the skin and let it dry before injecting. Do not rub the site afterwards. A little bruising or redness is common and usually fades; rotating sites each week reduces it. If you feel anxious about the needle, remember it is short and fine, and most people find the first injection is the hardest.
Needle anxiety is common and usually eases quickly. It can help to prepare everything in advance, sit comfortably, and breathe out as you inject. Many pens hide the needle entirely, so you never see it. If anxiety is stopping you from injecting at all, tell your pharmacy team; they can talk you through the device and technique. Once the routine is established, most people describe it as a quick weekly task rather than an ordeal.
Sharps disposal matters for safety. Used needles and pens go in an approved sharps bin, which your pharmacy can advise on, and full bins are returned through the proper route rather than put in household or recycling waste. Keeping the bin out of reach of children and never overfilling it are simple but important habits.
Storage away from home and temperature slips
If a pen is left out of the fridge, the in-use limit in your product information tells you how long it stays usable at room temperature. Beyond that, or if it has been very warm or frozen, do not use it and speak to your pharmacy. For trips, a small insulated bag keeps a pen cool, and our guide to travelling with GLP-1 medication covers flights, time zones and keeping to your weekly day.
If you miss a dose
Missed-dose rules depend on the medicine and how long ago the dose was due. Your product information sets out what to do; often a missed weekly dose can be taken within a set number of days, otherwise it is skipped and you carry on with your usual schedule. If you are unsure, contact your pharmacy or clinician rather than doubling up, since taking two doses close together can worsen side effects.
