What to expect.

When you first start taking Wegovy, Mounjaro, and other weight loss injections, it’s fairly common to experience some side effects at first. That’s because your body needs to adapt to the medication.

Many of these are fairly common, and will pass. But there are other, less common side effects, that you should also look out for.

If you experience any of the side effects listed as Rare on this page, don’t wait. Make sure you contact the relevant medical professionals immediately.

When Not to Worry.

Common Side Effects

It’s fairly normal to experience some side effects when you first start taking Wegovy or Mounjaro. Your body is going through a period of adjustment to a new medication, and so needs time to adapt – and that can mean the occasional hiccup along the way.

Any of the below side effects – while of course unpleasant – are generally considered normal, and should pass after a short period. You can help these by staying hydrated, getting plenty of fresh air, and eating a diet of simple, whole foods – nothing too rich, greasy, or flavourful.

Common Side Effects

At least one of these side effects is experienced by 1 in 10 people when they first start taking Wegovy or Mounjaro, as their body takes time to adapt to the new medication.

  • Heartburn and nausea
  • Constipation
  • Headaches
  • Vomiting
  • Diarrhoea
  • Injection site reactions

These can, for the most part, be managed safely at home with over the counter medications – and will pass within a few weeks.

Rare side effects.

While rare, it’s important to be aware of the potential steps you should take if you experience any of the below.

Pancreatitis

Symptoms: Severe abdominal pain, vomiting, indigestion, high fever, jaundice, rapid heartbeat.

What to do: Seek immediate medical advice by calling 111, or visiting 111.nhs.uk.

Hypoglycemia

Symptoms: Dizziness, blurred vision, irritability, slurred speech, sweating, weakness.

What to do: Drink a sugary drink and, if symptoms persist, contact 111.

Gallbladder Issues

Symptoms: Intense abdominal pain, fever, jaundice, itchy skin, confusion.

What to do: Contact your GP practice if symptoms persist.

Cancer Concerns

Symptoms: In rare cases, GLP-1 medications can cause thyroid goiters, particularly in patients with pre-existing thyroid disease.

What to do: Report any neck swelling to your GP practice.

Anaphylaxis

Symptoms: Difficulty breathing, swelling of throat/face, severe rash, rapid heartbeat.

What to do: Call 999 or go to A&E immediately.

Mother and Child in front of TV

Yellow Card Scheme

The Yellow Card Scheme exists to keep patients safe – so if you experience any unusual side effects, you can report them here to allow the MHRA (the UK’s medicines licensing body) to make sure these medicines continue to be prescribed safely.

Visit Yellow Card website
This page has been reviewed by:

Stephanie Smith – Lead Nurse
NMC number: 06I0726S

All the advice and guidance we provide is reviewed by a member of our clinical team – so you know what you’re reading is safe, and clinically accurate.