Weight-loss injections like Wegovy and Mounjaro are helpful tools for weight loss, but they need to be used properly to minimise the risks of mistakes and side effects. This article explains what “safe and appropriate use” means in practice, from the importance of the right prescribing route, to why online dosing hacks can be riskier than they sound, and what to do if cost, side effects or progress are making you consider changes to how you use your pen.
Wegovy and Mounjaro are prescription-only medicines
Weight-loss injections like Wegovy and Mounjaro are prescription-only medicines in the UK. That means they should be prescribed after a clinical assessment and supplied by a legitimate pharmacy.
UK guidance highlights the risk of misuse and the importance of using these medicines exactly as intended.
The Medicines and Healthcare products Regulatory Agency (MHRA), the UK medicines regulator, advises using them only when prescribed and supplied through appropriate routes. If you’re offered injections without a proper consultation, or from a non-medical setting, treat that as a red flag. UK authorities warn that GLP-1 products sold through illegal/unregulated routes may be fake, contaminated or incorrectly dosed, and can put people’s health at risk.
Off-plan dosing increases the risk of mistakes
You may see advice online about microdosing or taking a “custom” dose that doesn’t match the manufacturer’s instructions. This is not an authorised way to use weight-loss pens, and it increases the chance of dosing errors.
The manufacturer’s dosing schedule is designed to help your body adjust and to reduce side effects. When people try to “hack” the pen, the amount delivered can become less predictable, and side effects can be harder to manage.
Why “custom” doses are unsafe
Trying to adjust the pen yourself, for example, by half-pressing the button, reusing part of a dose, trying to retrieve an extra dose from your pen, or sharing pens, can:
- Damage the pen or needle
- Mean you get too much or too little medicine
- Increase the risk of infection
It also means you’re using the medicine in a way that wasn’t checked for accuracy and safety in clinical studies.
How to take GLP-1 medication
Here are step-by-step videos on how to inject GLP-1 medications:
- How to inject Wegovy
- How to inject Mounjaro
Always use your pen exactly as shown in the patient leaflet contained inside the box. Your prescriber should provide further guidance to ensure you understand how to use it.
If you’re not happy with your current dose because of side effects, how well it’s working, or cost pressures, speak to a healthcare professional. They can help you adjust safely or discuss alternatives, so you never need to experiment with the pen yourself.
Key messages
- Only use Wegovy/Mounjaro with a valid UK prescription from a regulated clinic or pharmacy
- Don’t adjust the dose yourself
- Use the pen exactly as instructed: don’t split doses, reuse leftovers, or share pens
- If you’re tempted to adjust because of cost or side effects, speak to a doctor first
What our clinical experts say
Whilst cheaper GLP-1 products may sound enticing, if they are not prescribed following proper clinical assessment and dispensed by a regulated pharmacy, patients could be exposed to serious harm. As prices increase at higher doses, the most cost-effective and safest approach is to use the lowest effective dose alongside meaningful lifestyle change, ideally with a plan to stabilise weight and cycle off treatment where lifestyle changes have been implemented.
Dr Caroline Butler
Genwell reflections
Using weight-loss medication safely is about more than the injection technique. It’s about making sure the treatment matches your needs, using it exactly as intended, and having support when questions come up.
At Genwell, we stay with you throughout your journey, helping you review what’s working and adjust your treatment as needed.