Taking 3.75 mg Mounjaro from Your 5mg Pen: What's Actually Happening

You're mid-titration and your prescriber has signalled a slower step up

Most people on Mounjaro follow a standard schedule: 2.5mg for four weeks, then 5mg, then up through 7.5mg, 10mg, 12.5mg and 15mg, each in roughly four-week increments. But that schedule isn't a rigid conveyor belt. Some people find the jump from 2.5mg to a full 5mg dose brings noticeable nausea or fatigue that makes daily life harder than it needs to be. In those cases, a prescriber might suggest pausing at an intermediate dose (3.75mg) giving the body more time to settle before reaching the licensed 5mg step.

It's worth being clear about what 3.75mg means physically. Each 5mg Mounjaro KwikPen is designed to deliver four equal doses of 0.625ml across four consecutive weeks. Three of those doses equal 3.75mg. So if your prescriber has confirmed this approach, you'd use three of the pen's four doses and then discuss what comes next before starting a new pen. The specifics of drawing 3.75mg from a 5mg pen cover the exact steps in more detail, and if your prescriber has instead directed you to start from the 2.5mg pen, the guide on reaching 3.75mg from a 2.5mg pen walks through how that works in practice.

The key thing to hold onto here: this is a clinical arrangement, not something to arrive at independently. The prescriber who knows your history, your current weight, and your response to treatment is the right person to confirm whether three doses from a 5mg pen is what's intended, or whether something else is meant.

What happens to the fourth dose left in your pen

This is the question that trips most people up, and reasonably so. If you use three of the four doses in a 5mg pen at 3.75mg total, one dose remains. What you do with that remaining dose depends entirely on what your prescriber has told you. Some people are advised to discard the pen after three doses and begin a fresh one; others may be instructed to continue to that fourth dose as part of their transition back to the standard 5mg step.

Never assume the right answer. Contact our clinical team or your prescriber directly if the plan wasn't spelled out. You can also find practical information through our FAQs or reach us via the contact page if you need to speak to someone quickly.

One straightforward check you can do right now: count the number of dose windows remaining on your pen's indicator (or the clicks used, depending on the pen variant you have). Most Mounjaro KwikPens have a visible dose counter. Spending thirty seconds confirming how many doses you've already taken will tell you immediately where you stand before your next injection day. That small habit prevents a common source of confusion.

Storage during this process follows the same rules as always: the pen stays refrigerated at 2–8°C when not in use. For the precise room-temperature window if you need to carry the pen with you, the Patient Information Leaflet included with your treatment is the right reference, the NHS tirzepatide medicines page also provides a clear patient-level overview of storage and handling.

Why this isn't the same as self-adjusting your dose

There's an important distinction between following a prescriber's confirmed plan for 3.75mg and deciding independently to use fewer doses because you're experiencing side effects or because a full pen feels like too much. The first is supervised clinical management. The second carries real risk, both of under-treating and of creating confusion when your prescriber next reviews your progress.

If you're finding the move to 5mg difficult and your prescriber hasn't yet discussed a slower step-up, that conversation is the right next move. It's one our prescribers have regularly, you can read more about how we approach clinical oversight on our about page or see the clinical team profile at our clinical team page. Prescribers can formally adjust your titration plan, which protects both the evidence trail and your safety going forward.

Mounjaro is a dual GIP and GLP-1 receptor agonist, the only medicine of its kind licensed in the UK for weight management. As the NICE technology appraisal for tirzepatide (TA1026) makes clear, the medicine's benefit relies on a properly managed dose trajectory, not just reaching a target dose as fast as possible. Slower titration when needed is evidence-aligned practice, not a workaround.

Moving from 3.75mg toward the full licensed schedule

Once you've spent the agreed time at 3.75mg and your prescriber is satisfied with your tolerance, the plan will typically be to complete the 5mg step before considering a move upward. If you haven't yet looked at what using a 5mg Mounjaro pen in full looks like, that page covers the standard use of that dose.

For context on what comes after 5mg (because many people wonder how long the titration continues) the guide on taking 5mg from a 7.5mg pen explains the next step in the sequence, which follows the same graduated logic.

The broader picture of Mounjaro as a treatment, including how the full dose schedule works from 2.5mg through 15mg, is covered on the Mounjaro treatment page. And if you've come to this page wondering whether 3.75mg is even a recognised approach rather than something your prescriber may have described loosely, the page on whether 3.75mg of Mounjaro is clinically recognised addresses that directly.

If you're not yet on treatment and are considering starting, a free consultation with our prescribers is the first step, they review every case individually and can advise on the right starting point for you. Speak to our prescribers to begin.