Are Weight Loss Pens Safe?

Both Mounjaro and Wegovy are prescription-only medicines (POMs) — meaning a qualified prescriber must assess suitability before they are dispensed. This is an important safety safeguard: it is not possible to obtain them without clinical oversight in regulated markets.

Regulatory status and ongoing monitoring

In many countries, including the UK, these medicines carry a black triangle symbol (▼), which means they are subject to additional monitoring. This does not imply they are more dangerous than other medicines; it means regulators are actively gathering more safety data as real-world use grows. Users are encouraged to report any suspected side effects to their national reporting scheme — for example, the UK's Yellow Card scheme — and to their own healthcare professional.

Commonly reported side effects

The most frequently reported side effects are gastrointestinal: nausea, vomiting, diarrhoea, constipation, indigestion, and reflux. Fatigue, headache, dizziness, burping, and injection-site reactions are also commonly noted. For many people these are mild and ease over time, particularly after the initial period at a new dose. They are not universal — individual experiences vary considerably.

Certain groups require particular caution or are not suitable candidates at all, including people with a personal or family history of specific thyroid conditions, a history of pancreatitis, or those who are pregnant or trying to conceive. Your prescriber will have assessed these factors before prescribing.

Not a quick fix

These medicines are not a cosmetic shortcut. They are prescription treatments used alongside dietary changes and physical activity, under clinical supervision. They are not suitable for everyone, and suitability is always a decision made by a prescriber. You can read more about how weight loss pens work and explore an overview of the options commonly discussed for more context.

One of the most useful things you can do while taking a weight loss pen is keep a clear, consistent record of how your body is responding — not just on the scale, but across energy, mood, sleep, and any side effects you notice. That record becomes genuinely valuable when you speak with your prescriber.

GLP Trackr's side-effect and symptom tracking lets you log how you feel day to day and spot patterns over time — for example, whether nausea clusters in the days immediately after a dose, or whether fatigue correlates with poor sleep. These patterns are easy to miss in the moment and useful to bring to a clinical appointment rather than trying to recall from memory.

Beyond symptoms, the app's weight and body tracking captures your progress week by week — weight, measurements, and trend charts — so you can see what's actually shifting rather than relying on a single weigh-in. A built-in daily check-in logs mood, energy levels, and food-noise alongside weight, giving you a rounded picture of your journey rather than just a number.

For a broader look at what tracking your journey involves, the weight loss tracking hub is a good starting point, and if you're researching the range of injectable options, this overview of weight loss pens covers the key differences.

If you experience any side effects that feel severe, persistent, or worrying at any point — including chest pain, severe abdominal pain, or significant mood changes — contact your healthcare professional promptly. GLP Trackr helps you record your journey; it is not a substitute for clinical advice, and any concerns about whether the medicine is right for you should always go to your prescriber or doctor.

Ready to start tracking the full picture? Download GLP Trackr on the App Store or Google Play — your first 7 days are completely free.