Weight Loss Injection Side Effects

In the UK, there are three weight loss injections approved for obesity treatment: Mounjaro, Wegovy, and Saxenda.

What about Ozempic?
Ozempic isn’t approved for weight loss in the UK—it’s licensed for diabetes. However, Wegovy contains the exact same active ingredient (semaglutide) and is made by the same manufacturer.

How do they work?
All three injections act on the GLP-1 receptor, a hormone that helps regulate appetite and blood sugar levels. Mounjaro goes a step further, also targeting the GIP receptor, which plays a role in metabolism. This dual action makes Mounjaro the most effective weight loss injection available.

Since Mounjaro and Wegovy target similar receptors, their side effect profiles are largely the same.

Side effects are common with both medications, but they are typically mild and resolve as the body adjusts. The most frequently reported adverse effects include:

• Nausea
• Diarrhoea
• Vomiting
• Constipation

These symptoms occur in more than 1 in 10 patients and are most prevalent during the initial weeks of treatment. If you have concerns about side effects or their management, Voy’s clinical team is available to provide guidance and support.

Generally speaking— you’re more likely to experience side effects as you take stronger doses of Wegovy or Mounjaro. But if you follow the dosing schedule, you’ll minimise your risk of getting them.
By starting on the lowest dose, you’re allowing your body to get used to the medicine so it can handle stronger doses later on. Then, if you’re tolerating the medicine okay, you’ll gradually move up to higher strengths. FYI: it’s completely fine to stay on lower doses, Wegovy and Mounjaro will still work.

The good news is that mostly, weight loss injection side effects are pretty easy to deal with.

Taking regular sips of a cold drink, or having a mug of ginger or peppermint tea, could help with nausea. For diarrhoea and vomiting, try resting and drinking plenty of fluids—eating only when you feel able to.

Try and avoid any potential trigger foods, such as spicy, rich or fatty foods. And cut down on alcohol, caffeine and fizzy drinks.

Eating smaller meals that are lower in fat can ease constipation. High-fibre foods like fruit and vegetables, oats and pulses can also help. For any symptoms that hang around or aren’t getting better, check in with your doctor.

Unfortunately, it’s impossible to say beforehand how your body will respond to Wegovy or Mounjaro. Some people experience no side effects, while others develop mild ones. And a far smaller proportion deal with something more severe. Everyone’s different, and your friend’s experience of weight loss medication may not reflect your own.

Mounjaro and Wegovy are both regulated and approved treatment for obesity in the UK. To ensure your safety, always get your prescription from a reputable provider registered with the UK General Pharmaceutical Council—you’ll find their registration displayed in a green box at the bottom of their website page.

It’s also important to choose a provider that gives you access to clinicians. At Voy, our in-house UK prescribing clinicians are always available to support you.