In this article
- • In brief
- • Why GLP-1 medication causes side effects
- • Which medicines does this cover?
- • What to do per symptom
- • Around a dose increase
- • Rare but important side effects
- • Checklist: these signs cannot wait
- • Surgery, anaesthesia or an endoscopy
- • How Go Leaner supports you
In brief
GLP-1 medication such as Ozempic, Wegovy and Mounjaro mainly causes gastrointestinal symptoms: nausea, a feeling of fullness, diarrhoea, constipation, vomiting or reflux. These symptoms are usually strongest at the start and around a dose increase, and then ease for most people.
There is a lot you can do yourself with smaller portions, eating slowly, less fat and spreading your fluid intake. But some symptoms are not something to simply 'push through'. At the bottom you will find a checklist of signs for which you call your doctor the same day, or 112.
Why GLP-1 medication causes side effects
GLP-1 is a gut hormone that enhances the feeling of satiety and slows gastric emptying. Medication that mimics this hormone therefore acts precisely in the digestive tract. Food stays in your stomach longer: you feel full sooner, but you may also feel nauseous or get belching. Bowel movement also changes, which leads to diarrhoea in some people and constipation in others.
That is why the dose is built up in steps. Your body gets a number of weeks per step to adjust. People who increase faster than the schedule usually get more symptoms, not faster results.
Which medicines does this cover?
'GLP-1' is often used as an umbrella term, but the medicines differ in active substance and indication. The type of side effects is largely the same; how often they occur depends mainly on the medicine and the dose.
Commonly used GLP-1 medicines
| Medicine | Active substance | Administration | Licensed for |
|---|---|---|---|
| Ozempic | Semaglutide | Once weekly, injection | Type 2 diabetes |
| Wegovy | Semaglutide | Once weekly, injection | Weight management |
| Mounjaro | Tirzepatide (GLP-1 + GIP) | Once weekly, injection | Type 2 diabetes and weight management |
| Saxenda | Liraglutide | Once daily, injection | Weight management |
What to do per symptom
In the STEP 1 study with semaglutide 2.4 mg (Wegovy), around 44% of participants reported nausea, 31% diarrhoea, 25% vomiting and 23% constipation, compared with considerably fewer in the placebo group. With tirzepatide (SURMOUNT-1), nausea (around 25 to 33%, depending on the dose) and diarrhoea (around 19 to 23%) were in the same order of magnitude. In both studies the symptoms were predominantly mild to moderate and occurred mainly during dose escalation.
For each symptom, the table below shows what you can try yourself and when to get in touch. These tips do not replace medical advice.
Checklist per symptom
| Symptom | What you can do yourself | Contact your doctor if… |
|---|---|---|
| Nausea | Eat small portions and stop as soon as you feel full. Eat slowly, avoid fatty and fried meals and do not lie down straight after eating. Drink in small sips spread over the day; some people find ginger or peppermint tea pleasant. | nausea means you are hardly eating or drinking, or if it does not ease after a few weeks. |
| Vomiting | After vomiting, take small sips of water or broth. Only eat again once you can keep fluids down, and then something light. | you vomit repeatedly, cannot keep anything down, pass little or dark urine, or become dizzy (risk of dehydration). |
| Constipation | Drink enough, increase fibre gradually (vegetables, fruit, wholegrains, legumes) and move daily. A fibre supplement such as psyllium can help; build up slowly and drink plenty with it. | you have had no bowel movement for more than a few days together with abdominal pain, a bloated abdomen or vomiting. |
| Diarrhoea | Drink extra to replace lost fluids. Temporarily eat lighter and less fatty food; watch out for coffee, alcohol and sweeteners if they make it worse. | it lasts more than a few days, or comes with fever, blood in the stool, severe abdominal pain or signs of dehydration. |
| Reflux and heartburn | Eat smaller and less fatty meals, do not eat too late or too heavily in the evening, and raise the head of your bed if you have symptoms at night. Limit alcohol, coffee and spicy food if these are triggers. | the symptoms are new and severe or persist. Use acid reducers only after consulting your doctor or pharmacist. |
| Fatigue, headache, dizziness | Make sure you drink enough, eat regular (small) meals and get enough protein. Stand up slowly. | you faint, are severely dizzy or symptoms persist. If you also use insulin or a sulfonylurea, consult your doctor straight away: the risk of low blood sugar is then higher. |
| Little appetite | This is partly the intended effect. Choose the protein source first at every meal so you preserve muscle mass. | you are structurally eating very little, losing muscle strength quickly or notice hair loss. |
Around a dose increase
Symptoms often increase in the days after a dose increase. That does not mean you should adjust the schedule yourself. Your doctor may decide to stay on the current dose for longer, postpone an increase or temporarily step back down. The goal is a dose that works and that you tolerate well, not reaching the highest step as quickly as possible.
Rare but important side effects
In addition to the gastrointestinal symptoms, the product information from the European Medicines Agency (EMA) lists a number of side effects that occur less often but that you need to recognise.
- Gallstones and gallbladder inflammation: rapid weight loss increases the risk of gallstones. Signs are pain in the upper right abdomen (often after fatty food), fever, yellow skin or eyes, dark urine or pale stools.
- Pancreatitis (inflammation of the pancreas): rare. The sign is severe, persistent pain in the upper abdomen that may radiate to the back, often with vomiting.
- Dehydration and kidney problems: persistent vomiting or diarrhoea can make you lose so much fluid that the kidneys suffer. Passing little urine and dark urine are warning signs.
- Severe allergic reaction: very rare, but acutely dangerous.
- Severely delayed gastric emptying: an extreme feeling of fullness after small amounts, or vomiting food hours later.
Checklist: these signs cannot wait
If you recognise one of the signs below, do not wait until your next appointment. If in doubt outside office hours, call the out-of-hours GP service (huisartsenpost).
Warning signs with GLP-1 medication
| Sign | What to do |
|---|---|
| Swelling of the face, lips, tongue or throat; shortness of breath or difficulty swallowing | Call 112 (the Dutch emergency number) immediately |
| Fainting or confusion | Call 112 (the Dutch emergency number) immediately |
| Severe, persistent abdominal pain, possibly radiating to the back | Doctor or out-of-hours GP service (huisartsenpost) the same day |
| Repeated vomiting or being unable to keep anything down | Doctor or out-of-hours GP service (huisartsenpost) the same day |
| Passing little urine, dark urine, severe dizziness | Doctor or out-of-hours GP service (huisartsenpost) the same day |
| Yellow skin or eyes, dark urine with pale stools | Doctor or out-of-hours GP service (huisartsenpost) the same day |
| Fever with abdominal pain | Doctor or out-of-hours GP service (huisartsenpost) the same day |
| Blood in stool or vomit | Doctor or out-of-hours GP service (huisartsenpost) the same day |
| Chest pain or severe palpitations | Call 112 (the Dutch emergency number) for chest pain; otherwise a doctor the same day |
Surgery, anaesthesia or an endoscopy
Because GLP-1 medication slows gastric emptying, your stomach may be less empty than expected during a procedure, even if you follow the fasting rules. This creates a risk of aspiration during anaesthesia or sedation.
Therefore always mention that you use GLP-1 medication before a planned operation, anaesthesia, gastroscopy or colonoscopy, or dental sedation. The anaesthetist or treating doctor decides whether you need to skip a dose or fast for longer. Do not change anything without that consultation.
How Go Leaner supports you
At Go Leaner you only start after an intake with a BIG-registered doctor in Amstelveen or Aalsmeer. The doctor reviews your medical history and medication, precisely to see whether there are factors that increase the risk of side effects, such as previous gallstones or pancreatitis.
During treatment you discuss symptoms with your doctor, who adjusts the titration schedule accordingly. So you do not have to wait and see whether side effects go away on their own: if symptoms persist, we look together at whether a lower dose, a slower build-up or a different medicine is a better fit.
Frequently asked questions
Related articles
Sources
- Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med 2021;384:989-1002.
- Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med 2022;387:205-216.
- EMA – Wegovy: product information (EPAR)
- EMA – Ozempic: product information (EPAR)
- EMA – Mounjaro: product information (EPAR)
This article provides general information about side effects of GLP-1 medication and is not personal medical advice. Always read the patient information leaflet of your medicine as well. Discuss symptoms with your treating doctor and call 112 (the Dutch emergency number) for acute, life-threatening symptoms.