Common Side Effects of Weight Loss Injections

Common Side Effects of Weight Loss Injections | UK Guide

If you are using Mounjaro or Wegovy, you may experience some side effects, especially when starting or increasing your dose. This guide explains the most common symptoms and what they usually mean.

What You’ll Learn

The most common side effects
Why they happen
How long they usually last
Which symptoms are considered normal

Why Side Effects Happen

Weight loss injections work by slowing digestion and reducing appetite. These effects can lead to temporary digestive symptoms while your body adjusts.

Side effects are most common when:

You first start treatment
Your dose increases

Nausea

Nausea is one of the most commonly reported side effects.

Often mild to moderate
More likely when starting or increasing dose
Usually improves over time

See How to Reduce Side Effects for ways to manage nausea.

Digestive Changes

Changes in digestion are also common.

Constipation
Diarrhoea
Bloating

These symptoms are usually temporary and improve as your body adapts.

Reduced Appetite

Reduced appetite is an expected effect of treatment and contributes to weight loss.

This may feel unusual at first but is part of how the medication works.

Fatigue

Some people experience tiredness, especially early in treatment.

Often improves with time
Can be linked to lower food intake

How Long Do Side Effects Last?

For many people, side effects are temporary.

First few weeks: More noticeable
After adjustment: Symptoms often reduce
Long-term: Usually mild or minimal

Are These Side Effects Normal?

Yes, mild digestive symptoms and appetite changes are common and expected.

However, if symptoms are severe or persistent, it is important to seek advice.

When to Look Closer

If something feels unusual or more severe than expected, it may be worth reviewing further guidance.