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Wegovy side effects

Robbie Puddick
Written by

Robbie Puddick

Medically reviewed by

Fiona Moncrieff

8 min read
Last updated May 2024

Jump to: Nausea and vomiting | Constipation and diarrhoea | Rare side effects | Take home message

The most common side effects of Wegovy are nausea, constipation, vomiting, and other symptoms affecting the gastrointestinal (GI) tract, like diarrhoea.

These symptoms most commonly occur around the time of the injection, during dose escalation, and are typically transient and will ease after you’ve adapted to the medication.

However, everyone responds differently to these medications; some people won’t experience any side effects, while others will have to discontinue their medication due to the discomfort the side effects cause.

While not cited in the literature, there are also reports of fatigue from taking Wegovy.

The mechanisms underlying this possible link to fatigue aren’t clear, but it could be an indirect effect of the drug lowering appetite and people not eating enough calories.

There are possible links to rare and more severe side effects such as pancreatitis and thyroid cancer. However, this has not yet been shown in the clinical trials for semaglutide.

However, there is no long-term data on Wegovy beyond two years, so we wouldn’t expect more severe side effects like this until more data is available.

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What is Wegovy?

Wegovy is a weight-loss medication that requires a weekly injection with semaglutide as the active ingredient.

Semaglutide is a GLP-1 receptor agonist that helps reduce hunger and appetite, allowing you to eat fewer calories, lose weight, and manage your blood sugar levels.

Wegovy is for individuals living with obesity to help them eat fewer calories and lose weight. You’ll also experience improved glycemic control due to the effect of GLP-1s on insulin function.

Wegovy was approved for weight loss in the UK in 2023 and Second Nature launched its Wegovy weight-loss programme in November of the same year.

Wegovys is taken once a week via a self-administered injection.

Not a magic pill

These medications are designed as additional tools for weight management interventions and shouldn’t be considered lifelong medications.

Instead, they should be used to help you kickstart your weight loss and healthy journey while you commit to living a healthier lifestyle.

At Second Nature, we’ve been trusted by the NHS since 2017 to support people with type 2 diabetes and obesity to lose weight and manage their blood sugar levels and lead healthier lifestyles for the long term.

In 2022, the NHS published data in the BMJ that compared the weight loss outcomes of five providers in the National Diabetes Prevention Programme.

Second Nature was more than twice as effective at supporting weight loss than the other four providers.

Otherwise, keep reading as we dig into the side effects of Wegovy and how to manage them.

1) Nausea and vomiting

Nausea is the most common side effect of Wegovy, with at least 25% of participants on GLP-1s experiencing it, with some studies showing up to 53% of participants reporting nausea at least once.

However, it’s typically transient and eases after the body has adapted to the medication or the higher dose you’ve started.

Vomiting is also common when taking semaglutide, with studies suggesting anywhere between 8-30% of participants will experience this at least once.

Both of these side effects are mainly attributed to the impact of GLP-1 medications to slow down gastric emptying and cause gut distension (enlargement). GLP-1s also communicate with our nervous system, which can disrupt signalling pathways leading to nausea.

These physiological effects mean that food takes much longer to pass through our digestive system.

Nausea and vomiting appear to be most common when people overeat or potentially overeat fat which also slows down gastric emptying and could further worsen symptoms.

Here are some tips to reduce nausea and the risk of vomiting on Wegovy:

  • Eat smaller meals
  • Eat slowly and mindfully
  • You might need to include snacks in-between your three main meals to ensure you’re eating enough
  • Stay hydrated
  • Avoid foods that previously made you nauseous
  • Record a food diary of foods you notice trigger symptoms
  • Eat simple meals based on a good source of protein, complex carbohydrates, fruit or vegetables, and some fat
  • Don’t lie down after your meal, maybe opt for a short walk
  • Avoid eating too close to bedtime
  • Speak to your doctor or prescribing physician if symptoms persist or become too uncomfortable

2) Constipation and diarrhoea

Constipation occurs in around 25% of participants taking semaglutide. Unlike nausea and vomiting, which are typically more transient, constipation (for those who experience it) appears to be a longer-lasting side effect of Wegovy.

Constipation may occur due to reduced muscle contractions in the colon when taking the medication.

Diarrhoea is also prevalent with Wegovy, with around 30% of participants experiencing this at least once.

It’s typically transient and should decrease as your body adapts to the medication. The causes of diarrhoea on Wegovy aren’t fully understood.

Surprisingly, much of the guidance to help constipation will also help manage and prevent diarrhoea.

Here are some tips to reduce constipation and diarrhoea on Wegovy:

  • Stay hydrated
  • Eat a wide variety of fibre sources (nuts, seeds, fruits, vegetables, legumes)
  • Exercise
  • Go to the toilet when needed (don’t try to hold it in!)
  • Adopt a proper toilet position and place your feet on a stool to help your bowel movements
  • Experiment with probiotics and fermented foods like yoghurt, kimchi, fermented beetroot, or kombucha
  • Speak to your doctor or prescribing physician if symptoms persist or become too uncomfortable

3) Rare side effects

Thyroid cancer and thyroid-related disorders

A recent meta-analysis (a study reviewing many studies on one topic) analysed the risk of thyroid cancer (and other thyroid-related conditions) associated with the use of GLP-1 receptor agonists like semaglutide (Wegovy) and liraglutide (Saxenda).

The results indicated that liraglutide (Saxenda) slightly increases the risk of thyroid-related disorders compared to a placebo.

This connection to the thyroid with liraglutide is well-documented in the literature, and individuals with a family history of thyroid cancers and related disorders shouldn’t take liraglutide.

Another GLP-1 dulaglutide was also shown to increase the risk of thyroid cancer and related disorders. It’s essential to note that these are rare side effects, and the overall risk is still minimal.

However, semaglutide (Wegovy) was shown to have no impact on the risk of thyroid-related disorders.

Despite this, current recommendations are the same as liraglutide and individuals with a history of thyroid disorders aren’t recommended to take semaglutide.

It’s likely that when more data becomes available, we’ll have a clearer picture of whether Wegovy affects thyroid function and the development of thyroid disorders.

Pancreatitis and pancreatic cancer

Despite the current guidelines against individuals with a history of pancreatic cancer or pre-existing pancreatic conditions, there’s no strong evidence that semaglutide, or other GLP-1 medications, increases the risk of pancreatitis, pancreatic cancer or other pancreas-related conditions.

A study analysed data from 100 randomised controlled trials on GLP-1s and found that 72 of those trials showed no difference between the incidence of pancreatic cancer or pancreatitis compared to the control groups.

Another study analysed the available data on randomised controlled trials that investigated the incidence of pancreatic cancer and pancreatitis on semaglutide specifically and showed no effect of semaglutide on pancreatic-related conditions.

Still, a potential link between pancreatic function and semaglutide can’t be completely ruled out. But based on the currently available data, it doesn’t seem to increase the risk of these conditions.

It’s possible that earlier associations between GLP-1s and pancreatic cancer and pancreatitis were confounded by the increased risk of these conditions in the baseline population of people living with type 2 diabetes who are prescribed these medications.

Additionally, using semaglutide has been shown to significantly improve insulin sensitivity and the ability of pancreatic beta-cells to produce and secrete insulin.

So, it’s likely that the benefits to glucose management and insulin sensitivity observed with semaglutide outweigh any potential risks associated with pancreatic cancer in the long term.


Interestingly, few of the major trials investigating the impact of Wegovy on weight loss and health report fatigue, tiredness, or lethargy as potential side effects.

However, there are widespread reports that fatigue is a very common side effect linked to its use.

One earlier phase 2 trial on higher-dose semaglutide (1.6mg) indicated that around 12% of participants reported fatigue whilst on the medication. But generally, it’s not a side effect reported in the larger phase 3 trials.

Whether this is due to poor reporting or the researcher’s decision that the fatigue isn’t associated directly with the medication is unclear.

It’s likely due to an indirect effect of the medication reducing appetite to a point where people don’t eat enough, and their bodies enter ‘starvation mode’ whereby metabolism effectively grinds to a halt to ensure sufficient energy delivery to vital organs.

Here are our top tips to prevent and manage fatigue on Wegovy:

  • Eat enough in your meals, and include snacks in between meals if needed
  • Ensure a source of protein at each meal
  • Aim to eat 5-9 servings of fruit and vegetables a day
  • Stay hydrated
  • Consider taking a multivitamin
  • Get daylight exposure, particularly in the morning
  • Aim to sleep 7-9 hours per night
  • Avoid caffeine after midday if you’re caffeine sensitive
  • Speak to your doctor or prescribing physician if symptoms persist or become too uncomfortable

Take home message

The recent innovations in GLP-1 medications are pretty remarkable and have caused quite a stir in the world of healthcare.

We’re in new territory where obesity and type 2 diabetes medications treat an underlying cause instead of merely treating the symptoms to support better management.

However, these drugs shouldn’t be seen as miracle cures; they’re not designed to be used for life.

They’ve been designed to be taken alongside lifestyle changes that will enable you to eventually come off the medications and maintain your lower weight for the long term.

The harsh reality is that we still don’t know the long-term effects of these medications on our health. There are examples of drugs being withdrawn from the market as more long-term data comes to light.

Lorcaserin was a weight loss drug approved by the Food and Drug Administration (FDA) in the U.S. but was recently withdrawn as data indicated that it increased cancer risk.

The example of lorcaserin is why you must weigh the pros and cons when your doctor prescribes medication or before you purchase it yourself and start treatment. Report any side effects to your healthcare team.

GLP-1s are safe and effective for most people in the short to medium term, but we don’t have long-term data to be sure they’re not causing severe adverse effects elsewhere.

If you’re considering taking Wegovy for weight loss, weighing up the pros and cons of the medications and understanding your experience will be different to others.

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