What happens if I accidentally use the fifth dose from my Mounjaro pen?

The pen is designed to only administer four doses, so you shouldn’t be able to accidentally inject a fifth. But some users have attempted to extract the leftover liquid using insulin needles. We need to stress: This is not safe. The remaining liquid is not intended for use and is no longer sterile. You’ll want to dispose of your Mounjaro pen after you’ve taken four doses.If you’ve already used the leftover liquid, please contact your clinician as soon as possible — they may need to review any symptoms or side effects, assess whether you received too much or too little medication, and adjust the timing of your next dose accordingly.

What should I do if I experience severe side effects after my fifth dose of Mounjaro?

Stop using the medication and seek medical advice immediately. The Mounjaro pen isn’t designed to provide a fifth dose, but if you’ve manually extracted the leftover liquid and experience severe side effects—like nausea, vomiting, dizziness, or signs of infection—a healthcare professional can assess your symptoms and guide you on the safest next steps.

If I accidentally inject an incorrect amount from a pen (either too much or too little), what should I do?

Use the visual guide above to track how many doses you have left in your pen—it can be useful if you're unsure whether you've administered too much or too little. If you think you may have used an incorrect amount, please contact a clinician for advice, as it may affect your dosing schedule and should be reviewed promptly to keep you safe.

How should I properly dispose of my Mounjaro pen after using all four doses?

Dispose of your Mounjaro pen in a sharps bin, or follow your local guidelines for medication waste. Do not reuse or attempt to extract any remaining liquid.

Are there any reported side effects or risks that specifically come from trying to extract a fifth dose from Mounjaro pens?

There are no official studies, but risks include bacterial contamination, inaccurate dosing, and increased side effects. It’s not a safe or approved use of the pen as per the manufacturer.

Mounjaro “Golden” (Fifth) Dose Explained

If you’re on a weight loss journey and have spent any time in online communities like TikTok, Reddit, or YouTube, you've likely heard of the so-called "golden dose" of Mounjaro—sometimes referred to as "the magic fifth dose."

Many weight loss medication users are asking: Can you really get an extra dose from a Mounjaro pen? And if so, is it safe?

Let’s break down what the "golden dose" actually is, why it's there, and whether or not it's a good idea to try and use it.

What is the Mounjaro "golden dose”?

When people talk about a “golden dose” of Mounjaro, they’re usually referring to a small amount of liquid left in the Mounjaro pen after taking the four prescribed doses.

Each Mounjaro pen contains 3ml of liquid, and each dose uses 0.6ml—just enough for four, accurate, pre-measured doses of Mounjaro. That leaves a small amount of liquid behind. The leftover liquid is not a bonus dose—it’s a deliberate overfill built into the pen to ensure complete delivery of each injection.

This is a standard practice with many injectable medications. The overfill ensures there’s enough liquid for a flow check before each dose and accounts for any small variances in delivery.

Take a look at the visual guide below. It shows you how to track the number of doses remaining in your Mounjaro pen—including what the pen looks like once all four doses have been used.

This can be useful if you’re unsure whether you've administered too much or too little.

Visual progression of a Mounjaro KwikPen after each weekly dose: full pen, then pen levels after one, two, three, four, and the final ‘golden’ fifth dose — showing medication volume decreasing with each use.

Need a little more guidance on how to correctly take your weight loss medications? We’ve got you. See Voy’s guide to injecting Mounjaro.

Can you use the fifth dose of Mounjaro and is it safe?

The short answer is: No, and it’s not recommended.

Using a so-called fifth dose can come with serious risks, so clinicians and Mounjaro’s manufacturer strongly advise against it.

Risks of using the fifth dose

Underdosing: The leftover liquid is not a full, measurable dose. Using it may result in underdosing, which can reduce the effectiveness of your treatment and impact your weight loss progress.
Overdosing: Without dose control, you may inject too much, increasing the risk of Mounjaro side effects like nausea, vomiting, diarrhoea, or constipation.
Loss of sterility: Once the Mounjaro KwikPen is used, it expires after 30 days. After this period, it must be discarded, as it might no longer be free of germs. Attempting to extract and use the remaining medication can introduce bacteria and increase the risk of infection.

For these reasons, it’s just not worth attempting to use “the golden dose” of Mounjaro.

How to get the "golden dose” of Mounjaro

We understand the motivation behind this question—it can feel like wasted medication.

But the leftover liquid isn’t meant for dosing. It exists to ensure accurate delivery of the prescribed amount and to provide enough for flow checks during injection.

Anecdotally on online forums, some users have reported trying to extract the remaining liquid using insulin syringes in hopes of accessing a “fifth dose.” But this practice is not safe or medically supported.

We know we sound like a broken record, but it’s really important that you do not attempt to extract a fifth dose from your Mounjaro pen. Instead, follow the prescribed dosage schedule of one dose every four weeks.

If you’re unsure about your current dose or feel it isn’t working as expected, speak to a clinician. Self-adjusting can lead to underdosing, overdosing, or side effects.

Side effects support at Voy

"If you're using Voy and you experience any side effects, rest assured that our expert clinicians are just a message or phone call away. They can adjust your dose, prescribe medication to ease your symptoms, or simply offer reassurance.

Everyone responds differently to weight loss treatment and we'll help you find what feels right for you."

Phoebe Fox - Weight Loss Specialist Clinician

Final thoughts

The idea of a "golden dose" may be tempting, but safety comes first. The leftover liquid in your pen is not a secret fifth dose, and trying to use it can lead to inaccurate dosing, contamination and serious side effects.

At Voy, we believe in safe, clinically supported weight loss using licensed GLP-1 weight loss medications. If you have questions about your medication, dosage, or results, chat with your clinician. They’ll be happy to give you personalised advice.

Curious to know if Mounjaro can help you reach your health goals? We’re here for you every step of the way. In our weight loss programme, you can get weekly medication, ongoing support from our team of experts, plus access to an app to help you stay on track. Find out if you’re eligible by taking this short quiz. We’ll get back to you asap.

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Ready to take the next step in your weight loss journey? Learn more about Mounjaro and how Voy’s new approach to weight management could help you meet your health goals.