WEIGHT MANAGEMENT ∙ 3 minutes read

What are the most common side effects of semaglutide?

By Dr Jaskirt Matharu

Semaglutide, the active ingredient in Ozempic and Wegovy, has proven to be an effective and safe treatment for type 2 diabetes in the UK and has also been recommended by the National Institute for Health and Care Excellence (NICE) as a treatment for weight loss. But as with all medications, some people may experience side effects. Here is all you need to know about the side effects of semaglutide: what the mechanisms behind them are, how long they last, and what you can do to relieve them.   

How does semaglutide work?

Semaglutide belongs to a group of drugs called glucagon-like peptide-1 (GLP-1) agonists, meaning that it mimics the GLP-1 hormone that we all have in our bodies. When we eat, GLP-1 is released in the gut which mainly impacts two parts of our body: 

  • The stomach: GLP-1 makes the stomach digest food slower so that the food stays in the stomach longer. This makes you feel fuller faster and for longer.  
  • The brain: GLP-1 enhances satiation, which reduces food intake, appetite, and feelings of hunger.

These two mechanisms collectively reduce your appetite, leading to reduced food intake. This is how semaglutide, a synthetic form of GLP-1, aids weight loss. 

But the process of delaying digestion in the stomach can also cause discomfort in the gastrointestinal system, resulting in side effects.  

What are the most common side effects of semaglutide?

If you’re taking any medication for the first time, make a habit of always reading the patient information leaflet that comes with the medication. It lists any potential side effects and warnings so that you can be well informed before you start taking it.

Most of the common side effects of semaglutide cause discomfort in the gastrointestinal system, including: 

  • Nausea (feeling sick)
  • Diarrhoea
  • Vomiting 
  • Constipation
  • Stomach pain
  • Bloating
  • Gas
  • Upset stomach
  • Heartburn

Some other common side effects you may experience include:

  • Headache
  • Fatigue (a feeling of tiredness and lack of energy)
  • Dizziness

Some of these side effects may actually be a consequence of the gastrointestinal side effects - for example, headaches can be caused by dehydration which can occur as a result of severe vomiting and diarrhoea. 

How long do the side effects of semaglutide last?

The length of time that people experience side effects varies from person to person. Some people won’t have any side effects and will be able to tolerate the medication straight away. Others might experience side effects from the beginning that go away after a while.  

Most of the common side effects of semaglutide are mild and will only last for a few weeks as your body adjusts to the medicine. The side effects are most common during the period when the dose is increased. To ease this period, the first dose of semaglutide will be low, and will then be gradually increased to the optimal dose.  

What are the more serious side effects of semaglutide?

Semaglutide is a prescription medication, so it won’t suit everyone, and as with a lot of medications, there's the potential for serious side effects that you should be aware of. The patient information leaflet states that semaglutide should not be used by people with type 2 diabetes who take any other medication for diabetes because of the risk of hypoglycemia (low blood sugar). There is also a risk of pancreatitis (inflammation of the pancreas), which causes severe, persistent stomach pain.

Some initial studies of semaglutide showed an increased risk of thyroid tumours including cancer when the medication was tested on rodents. These laboratory animals have an innate higher risk of developing thyroid cancer, which humans don’t seem to have to the same extent. This means that the risk of developing thyroid cancer after the use of semaglutide does not seem to be increased in humans. As a precautionary measure, semaglutide is not prescribed if you or any of your family have ever had a type of thyroid cancer called medullary thyroid carcinoma (MTC) or if you have multiple endocrine neoplasia (MEN) type 2. 

If you experience any of the serious side effects listed above, contact your healthcare provider immediately. During your consultation, you will have the opportunity to talk to a clinician and tell them about your medical history, which will help them make an informed decision regarding which weight loss treatment would best suit you. 

What should I do if I experience side effects from semaglutide?

If you do experience side effects of semaglutide, there are a few things you can do: 

  1. Don’t eat too much food: try to only eat as much food as you need to feel full. Over-eating while taking semaglutide increases the risk of gastrointestinal side effects.   
  2. Ask about changing your dose: if the side effect is affecting the gastrointestinal system, for example, nausea, the increase of your dose can be delayed. This gives the body some extra time to adjust to the medication. Another option is to lower your dose until the symptoms improve.
  3. Drink plenty of water: in case you have diarrhoea or constipation, you should drink plenty of water to avoid getting dehydrated.
  4. Use over-the-counter medication: there are a number of medications that can relieve symptoms of nausea, heartburn, and headache that are available over-the-counter. Ask at your local pharmacy if you’re unsure about which is best for you.
  5. Ask about switching medication: in case you experience side effects that are too bothersome to tolerate, there is the option of asking to switch to a different medication.

If you’re concerned about any side effects, make sure to contact your health practitioner for advice. They'll help guide you on which of the options listed above are the most appropriate for you and your symptoms.

The bottom line

If you do experience side effects while on treatment with semaglutide, don’t despair. Follow our advice to guide you on your journey to a better, healthier, and lighter life.