Weight Loss Injection Side Effects & Best UK Price Compare

Weight loss injections are helping people lose weight, feel confident, and take control of their health. But it’s also a reality that they can cause some side effects over time. Whether you’re starting new or thinking about shifting treatments, it’s important to be aware of the potential risks that come along with the benefits.

In this blog, we’ve put together the most common side effects of popular weight loss injections, so you can understand what to expect if you decide to start this journey. But first, let’s look at which weight loss injections are available in the UK and how they actually work.

What Are Some Popular Weight-Loss Injections in the UK and How Do They Work?

Most weight-loss injections in the UK help people lose weight by working with the body’s natural hormone system. They mimic their process and help the body control hunger and keep it full for a long time. When paired with lifestyle changes, they can prove to bring even better results. Most people are advised to increase physical activity, keep hydrated, eat mindfully, prioritise sleep, manage stress, and more, depending on the situation.

There are two main types of weight-loss injections available in the UK:

GLP-1 Receptor Agonists:

These mimic a hormone called glucagon-like peptide-1 (GLP-1), which helps control appetite, slows down digestion, and stabilises blood sugar.

Common GLP-1 injections include:

1. Wegovy (semaglutide)
2. Saxenda (liraglutide)

Dual GIP/GLP-1 Receptor Agonists:

Together, they form a combo that can be more effective at weight loss, especially in people who haven’t seen strong results with GLP-1 medications alone.

Mounjaro (tirzepatide) is the most prominent example currently available. Clinical studies have shown that it can be helpful in reducing about 20-25% weight over 72 weeks when combined with healthy lifestyle changes. 

Each of these medications works a little differently, and the side effects can vary too. Let’s take a closer look at what people typically experience when starting these injections.

What Are the Common Side Effects of Popular Weight-Loss Injections in the UK?

The side effects of weight-loss injections vary from person to person, but certain patterns do emerge.

Many people report mild symptoms in the first few weeks, but they normally fade as the body adjusts. But for some, these can be more persistent, especially during dose increases or if the injection isn’t paired with the right lifestyle habits. 

To understand the fuller picture, let’s look at how each injection tends to affect people. 

Wegovy (Semaglutide)

A 2021 study in The New England Journal of Medicine found that over 70% of participants reported gastrointestinal symptoms during treatment, with nausea being the most frequent.

Some common side effects of Wegovy include:

• Nausea, especially during the dose escalation phase
• Constipation or diarrhea
• Bloating or burping
• Fatigue
• Headaches

Mounjaro (Tirzepatide)

The SURMOUNT-1 trial, published in The New England Journal of Medicine in 2022, reported that nausea (24.6–33.3%), decreased appetite, and constipation were the most frequent side effects. Fatigue was also noted in some patients during early weeks of treatment. 

Some common Mounjaro side-effects include:

• Nausea or upset stomach
• Reduced appetite (sometimes more pronounced than other medications)
• Constipation
• Fatigue
• Light-headedness or mild dizziness

Saxenda (Liraglutide)

According to a 2015 study in The Lancet, gastrointestinal side effects like nausea and dyspepsia were the most frequently reported among Saxenda users, especially at the beginning of treatment.

Here are some of the common Saxenda side-effects::

• Nausea and stomach discomfort
• Burping or acid reflux
• Injection site irritation
• Headaches
• Slight increase in heart rate in some individuals

Most people say these side effects don’t last long and usually get better after a few weeks. Eating smaller meals, skipping oily foods, and drinking plenty of water can make things easier. But if the symptoms don’t go away or feel too strong, it’s a good idea to talk to a doctor.

How to Reduce the Side Effects?

While side effects can’t always be avoided, many people find they become easier to manage with a few adjustments. Here are some tips that can prove to be worthy:

1. Start slow: Never rush your dose increases. When you gradually increase your doses, it helps your body adjust more gently.
2. Stick to lighter meals: Greasy or heavy foods can make symptoms like nausea worse. Plain, protein-rich meals usually sit better.
3. Stay hydrated: Drinking enough water throughout the day can help ease headaches, fatigue, and digestion-related issues.
4. Avoid lying down after eating:  Give your body time to digest. This can reduce bloating, reflux, and nausea.
5. Keep moving: Gentle physical activity like walking after meals can help improve digestion and reduce sluggishness.

What’s the Science Behind These Side Effects?

These medications work by mimicking hormones that help regulate appetite and digestion. When those hormones are activated, your stomach empties more slowly, your brain gets the signal that you’re full sooner, and your cravings naturally decrease.

But this shift can cause some temporary discomfort. Feeling full faster might lead to nausea. Slower digestion can mean bloating or changes in bowel movements. And since you're likely eating less than usual, it’s not uncommon to feel a bit tired or low on energy, especially in the early days.

That is why the body adjusts over time, and these effects either disappear or become much easier to manage. It’s just part of the process as your system learns a new routine.

Are There Any Long-Term or Serious Side Effects of Weight Loss Injections?

While most people only experience mild and temporary side effects when starting weight loss injections, there are a few serious or long-term risks you should know about. These don’t happen to everyone, and in many cases, they are rare. But it’s important to be informed before starting any new treatment.

Here are some of the long-term side-effects:

Mounjaro (tirzepatide):

• Thyroid C-cell tumors (in animal studies)
• Pancreatitis
• Gallbladder problems
• Kidney issues (if dehydration isn’t managed)
• Severe or long-lasting digestive issues
• Ongoing fatigue or reduced appetite

Wegovy (semaglutide):

• Pancreatitis
• Gallbladder issues
• Kidney function changes
• Increased heart rate 

Saxenda (liraglutide):

• Pancreatitis
• Gallstones or gallbladder inflammation
• Kidney problems (especially with dehydration)
• Increased resting heart rate

Who Should Be Cautious?

While weight-loss injections can be incredibly effective for many people, they’re not the right fit for everyone, and that’s okay.

These medications are usually prescribed to people with a higher BMI or weight-related health concerns, but even then, certain health conditions need to be considered before starting treatment.

You should speak to a doctor first if you:

• Have a history of pancreatitis
• Have or had thyroid cancer, especially medullary thyroid carcinoma (MTC)
• Are living with gallbladder disease
• Struggle with severe digestive issues
• Are taking insulin or medications that affect blood sugar
• Are pregnant, breastfeeding, or trying to conceive

Final Thoughts

Weight-loss injections are helping a lot of people who’ve struggled to lose weight in the past. When used with healthy habits, they can really make a difference.

However, side effects can happen, especially in the beginning. But most people find that they get better with time. Having proper knowledge can help you feel more prepared and keep going.

If you’re thinking about starting, Mango Compare can help you find the best prices from trusted UK pharmacies so you don’t have to spend hours searching.

Compare prices and take the next step toward feeling better in your body.

FAQs

1. What are the most common side effects of weight loss injections like Wegovy and Saxenda?The most common side effects include nausea, diarrhoea, constipation, and vomiting. These usually occur in the first few weeks and often ease as your body adjusts. Headaches and tiredness are also reported by some users.
2. Which weight loss injection has the least side effects?Side effects vary by person, but Saxenda (liraglutide) is often considered milder for some users compared to higher-dose options like Wegovy or Mounjaro. Always consult your GP for the best choice based on your health.
3. Can weight loss injections cause nausea or vomiting?Yes, nausea and vomiting are very common, especially when first starting or increasing the dose. Eating smaller, low-fat meals and staying hydrated can help reduce these symptoms.
4. How long do the side effects of weight loss injections last?Mild side effects like nausea or bloating typically last a few days to a few weeks. Most people report that symptoms fade as the body adapts to the medication.
5. Why do GLP-1 injections cause digestive issues?GLP-1 medications slow down digestion and make you feel full longer. This change can lead to side effects like nausea, constipation, or diarrhoea, especially in the early weeks of treatment.
6. Can weight loss injections affect mental health or mood?Mood changes are not common but have been reported in some cases. Always speak to your doctor if you experience anxiety, low mood, or emotional shifts while using weight loss injections.