Welcome to your GLP-1 guide

No, not everyone experiences side effects. However, digestive side effects like nausea, vomiting, diarrhoea and constipation are very common with Wegovy and Mounjaro, affecting more than 1 in 10 people. How bad these symptoms are depends on the person, the dose and medication type. The good news is that most patients find that digestive side effects usually improve within a few days to a week.

To figure out if your side effects are caused by your treatment, pay attention to when they started, how they feel and how strong they are.

Nausea, vomiting, diarrhoea, constipation and stomach pain are the most common side effects of GLP-1 medications. These symptoms often appear when you first start treatment or increase your dose, but usually improve as your body adjusts to the medication.

These symptoms could indicate pancreatitis, a serious condition that requires urgent medical attention.

• Severe, persistent stomach pain. Severe means:

  • It’s so intense (around 8 or more out of 10) that you can’t focus on anything else

  • It makes it nearly impossible to handle normal daily tasks (like walking, getting dressed, or eating)

  • It doesn’t improve with over-the-counter pain relief or rest

  • It radiates to your back or underneath your right ribcage or your right shoulder

  • You also have severe vomiting (3 or more times a day, or having blood or something that looks like coffee grounds in vomit)

If you experience any of the following, stop taking your medication immediately. These symptoms could indicate anaphylaxis or a severe allergic reaction that requires urgent medical attention.

• Difficulty breathing, or swelling of the lips, tongue, or throat - these could be signs of a severe allergic reaction, which can be life-threatening.
• Severe pain underneath your right ribcage that may spread to your shoulder or back. This may be accompanied by vomiting, a high temperature or a rapid heartbeat. These symptoms could suggest acute gallbladder problems.

• Make sure you tell them you have been taking weight loss medication.

• Inform your MedExpress clinical prescriber.

• If you are using oral contraception and have experienced vomiting within 3 hours of taking your oral contraceptive pill, or diarrhoea that has lasted for over 24 hours, you may need a repeat dose of your pill to avoid an unwanted pregnancy. You should contact your GP or call 111 for medical advice.

Everyone responds differently to weight loss medications like Mounjaro and Wegovy, so the timeline for experiencing side effects can vary from person to person.

It’s common to notice some side effects when you first start taking these medications or after an increase in your dosage. This happens because your body is adjusting, and these side effects usually subside within a few days to a couple of weeks. Most people find these temporary issues manageable at home.

When increasing your dose, you may experience a temporary increase in side effects, such as nausea or stomach upset, as your body adjusts to the medication. These symptoms usually improve within a few days to a week.

Yes, most digestive side effects from GLP-1 treatments get better with time. In clinical trials, less than 5% of people discontinued GLP-1 medications because of side effects and despite people experiencing side effects in the study, many went on to complete their weight loss goals.

You might not be able to prevent side effects but you can reduce their severity by making a few simple lifestyle changes. We recommend reducing your fatty and ultra processed food intake, hydrating well and avoiding spicy food that might irritate your stomach.

Skipping doses to manage side effects is generally not recommended, as it can affect your treatment’s effectiveness.
If side effects become uncomfortable, speak to our clinical team. They may suggest adjusting your dose or offering practical tips to help you manage symptoms more comfortably.

Over-the-counter supplements can’t prevent side effects. However, they may help manage mild symptoms.

At MedExpress, we offer a range of supplements that may help with side effects.

Glucomannan Fibre is a type of prebiotic fibre. Taken before each meal, it can help to support weight loss and maintain normal cholesterol levels.

Support your muscle and bone health during your weight loss journey with our Magnesium Citrate supplement. Taken once daily, magnesium can also help to support heart health and reduce tiredness.

Our Psyllium Husk supplement is designed to help promote fullness, support regularity and regulate blood sugar spikes.

Very common (can occur in more than 1 in 10 people taking Mounjaro or Wegovy).

• What is it?

  Nausea is an uncomfortable feeling in your stomach that can make you feel like you might vomit. It’s often described as a queasy sensation, like your stomach is churning or feeling sour. It can make you feel very unsettled or ‘off’.

• Why does this happen?

  Your treatment works by slowing down how quickly your stomach empties, which helps you feel fuller for longer. Nausea can occur because the food stays in your stomach longer and causes your stomach to stretch. This triggers signals that send a message to the brain, making you feel nauseous.

• Here’s what we recommend:

  • Drink plenty of fluids (cold water, herbal teas)

  • Get lots of fresh air

  • Eat small and frequent meals

  • Reduce intake of foods high in sugar and fat

  • Avoid cooking or eating strong smelling foods

These strategies help with nausea by calming the digestive system and reducing triggers that can make it worse.

Very common (can occur in more than 1 in 10 people taking Mounjaro or Wegovy).

• What is it?

  Vomiting is when your body forcefully pushes the contents of your stomach out through your mouth, usually after feeling nauseous. It can feel like a pressure in your stomach, as your muscles contract strongly to force the contents of your stomach up. Many people feel a sudden sense of relief once it’s over.

• Why does this happen?

  Your treatment works by slowing down how quickly your stomach empties, which helps you feel fuller for longer. However, this can cause vomiting, just like it can cause nausea, because the food stays in your stomach longer and causes it to stretch. This triggers signals that are sent to the brain, which may lead to vomiting.

• Here’s what we recommend:

  • Stay hydrated by taking small sips of water. You could also try herbal teas such ginger and peppermint.

  • Eat small and frequent meals to keep your energy levels up. Stick to a bland diet that is easy on your stomach, such as toast, rice and bananas.

Very common (can occur in more than 1 in 10 people taking Mounjaro or Wegovy).

• What is it?

  Diarrhoea is when you have frequent, loose or watery stools. You might feel sharp or dull discomfort in your stomach, which often gets worse just before you need to go to the bathroom. You may have an urgent need to go to the toilet more than three times a day.

• Why does this happen?

  Diarrhoea can happen while using GLP-1s because the medication slows down how quickly food moves through your stomach, which can disrupt normal digestion.

• Here’s what we recommend:

  • Drink plenty of fluids (water, herbal teas)

  • Eat small and frequent meals

  • Rest – take it easy and allow your body to recover

  • Consider taking oral rehydration salts from a pharmacist to replace lost fluids and electrolytes

  • Paracetamol for pain relief

Very common (can occur in more than 1 in 10 people taking Mounjaro or Wegovy).

• What is it?

  Constipation occurs when it’s difficult to pass stool and you have fewer than three bowel movements in a week. The stools are often dry, hard or lumpy - sometimes resembling pellets or marbles - because your colon has absorbed too much water. This can lead to pain or discomfort when trying to pass stool.

• Why does this happen?

  Your treatment can cause constipation due to slowing down the movement of food and waste through your digestive system.

• Here’s what we recommend to help you:

  • Drink plenty of fluids (water, herbal teas)

  • Eat high-fibre foods such as prunes, figs, and oats

  • Take regular walks – exercise can stimulate bowel movements.

  • Consider glucomannan supplements – glucomannan is a water soluble fibre that softens stools to make them easier to pass. It can also help with regular bowel movements.

Very common (can occur in more than 1 in 10 people taking Wegovy).

• What is it?

  A headache is when you feel pain or discomfort in your head, scalp or neck. The feeling can vary depending on the type of headache. It might feel dull, achy or pressure-like. Common areas where you might feel it are your forehead, temples or the back of your head. It can also affect both sides of your head.

• Why does this happen?

  Your treatment causes the likes of vomiting and diarrhoea, which lead to fluid loss and dehydration which is a major cause of headaches. Your treatment also directly slows down how quickly food leaves your stomach, which can also affect hydration levels and how your body absorbs nutrients, increasing the risk of headaches.

• Here’s what we recommend:

  • Drink plenty of fluids (water, herbal teas)

  • Use simple pain relief like paracetamol

  • Apply a hot or cold compress

  • Ensure you are getting enough sleep – aim for 7–9 hours a night

Very common (can occur in more than 1 in 10 people taking Mounjaro or Wegovy).

• What is it?

  Stomach pain refers to discomfort or aching felt anywhere in the abdomen. There are different types of stomach pain but how you manage the pain depends on the type you’re experiencing.
  Trapped wind usually feels like bloating or pressure in your stomach, sometimes with burping or gas.

• Here’s what we recommend:
  • Eating smaller meals more frequently
  • Chewing food slowly
  • Going for a walk to stimulate bowel movements
  • Drinking peppermint tea

Stomach cramps usually feel like sharp, intermittent pains that often come in waves.



• • Avoiding spicy or greasy foods
  • Holding a heat pack to your stomach
  • Chewing food slowly

Dull or aching stomach pain usually feels like constant low level ache in either the upper or lower abdomen.



• Here’s what we recommend:
  • Eating smaller meals more frequently
  • Going for a walk to stimulate bowel movements
  • Using over-the-counter antacids

Common (can occur in up to 1 in 10 people taking Mounjaro or Wegovy).

• What is it?

  Injection site reactions refer to localised skin responses that occur after an injection. Symptoms often present within 24 to 48 hours of injection and may include pain, redness, swelling, warmth, itching, bruising or tenderness at the injection site.

• Why does it happen?

  They happen because the body is responding to the injection itself, the medication, or how it was administered.

• Here’s what we recommend:
  • Rotate your injection site each week. You can alternate between different areas such as your lower stomach, thigh, arm, and buttocks. This helps prevent irritation.
  • Make sure you’re correctly injecting your medication

Wegovy: Very common (affects more than 1 in 10 people).

Mounjaro: Common (can occur in up to 1 in 10 people).

• What is it?

  Fatigue is a persistent, overwhelming tiredness or lack of energy that lingers even after rest, making it difficult to perform daily tasks and activities.

• Why does it happen?

  You may experience fatigue while taking GLP-1s because of your reduced calorie intake, dehydration, and blood sugar fluctuations.

• Here’s what we recommend:
  • Make sure you are eating enough nutrient-dense food to get the calories you need for energy
  • Ensure you are getting enough vitamins. For example, vitamin B12 (found in meat, fish, cheese, and eggs) is important for energy production. Low vitamin D levels are also linked to fatigue, and while sunlight is the best source of this vitamin (we recommend that you always wear SPF 50 sunscreen), it is also found in oily fish, red meat, liver, and egg yolks
  • Check your iron levels, as low levels can cause fatigue. Iron is found in liver, red meat, and beans such as red kidney beans, edamame beans, and chickpeas
  • Exercise regularly to boost energy
  • Try to stick to the same sleep schedule and aim for 7 to 9 hours of sleep a night.
  • Have a relaxing sleeping area (not too bright, noisy, or warm)
  • Vitamin supplementation

Common (can occur in up to 1 in 10 people taking Mounjaro or Wegovy).

• What is it?

  Burping, also known as eructation, is when gas is released from your stomach and comes out through your mouth, often with a noticeable sound. It is a normal way for your body to get rid of air that you have swallowed while eating or drinking.

• Why does it happen?

  Your treatment slows down how quickly food leaves your stomach, meaning that food stays in your stomach for longer. As a result, gas can build up during digestion and may be released through burping.

• Here’s what we recommend:
  • Eat and drink slowly to help reduce the amount of air you swallow
  • Avoid fizzy drinks
  • Avoid chewing gum and sweets
  • Take regular walks - exercise can aid digestion and improve bloating

Common (can occur in up to 1 in 10 people taking Mounjaro or Wegovy).

• What is it?

  Heartburn is a burning sensation in the chest or throat caused by stomach acid backing up into the oesophagus. It typically feels like a burning sensation behind your breastbone or a sour taste in your mouth.

• Why does it happen?

  Your treatment slows down how quickly food leaves your stomach. As a result, food stays in the stomach for longer, which can increase the chance of acid reflux. Acid reflux is when stomach acid moves backward into the food pipe and causes heartburn.

• Here’s what we recommend:
  • Reducing your caffeine intake
  • Don’t eat too close before you go to bed
  • Avoid rich, spicy, or fatty foods
  • Heartburn medication

Common (can occur in up to 1 in 10 people taking Mounjaro or Wegovy).

• What is it?

  Dizziness can feel like a range of sensations, including lightheadedness, feeling unsteady, faint, or as if your surroundings are spinning (vertigo).

• Why does it happen?

  You may experience dizziness on GLP-1s due to changes in blood sugar levels and dehydration.

• Here’s what we recommend:
  • Drink plenty of fluids (water, herbal teas)
  • Lie down until the dizziness passes
  • Move carefully and slowly
  • Get plenty of rest
  • Avoid coffee, cigarettes and alcohol

Common (can occur in up to 1 in 10 people taking Mounjaro or Wegovy).

• What is it?

  Hair loss occurs when the normal cycle of hair growth is disrupted and is typically due to telogen effluvium - a type of hair loss that leads to increased shedding all over the scalp. Telogen effluvium feels like sudden, excessive hair shedding, often noticeable when brushing, washing, or running your fingers through your hair.

• Why does it happen?

  Hair loss while using Mounjaro or Wegovy is typically triggered by rapid weight loss (like that caused by GLP-1s). Rapid weight loss can cause hair loss because your body sees it as a form of stress. Your body will temporarily pause things that it doesn’t see as critical, like hair growth. This type of hair loss is usually temporary and hair will often grow back once your body adjusts.

• Here’s what we recommend:
  • Aim for a gradual and steady weight loss of 0.5-1kg per week to reduce stress on your body.
  • Ensure your diet includes sufficient amounts of protein, iron, zinc, and B vitamins (like biotin), which are essential for hair growth.
  • Manage stress, as high stress levels can disrupt hair follicle function. Focus on relaxation techniques like meditation, gentle exercise, or breathing exercises.
  • Once your weight stabilises, this side effect usually subsides and your hair should regrow to its original thickness.

Wegovy: Common (affecting up to 1 in 10 people).
Mounjaro: Uncommon (affecting fewer than 1 in 100 people).

• What is it?

  The gall bladder is a pear-shaped organ that sits near your right ribcage. Gallstones are hardened deposits of bile or cholesterol that form in the gallbladder.
  Gallstones don’t usually cause any symptoms, and many people don’t realise they have them.

• Why does it happen?

  Your treatment can result in rapid fat loss. When this happens, the liver releases extra cholesterol into bile - a fluid stored by the gallbladder that helps to digest fat. When there is too much cholesterol, it can form crystals that turn into stones. On top of that, weight loss can slow down how quickly the gallbladder empties, which gives gallstones more time to form.

• Here’s what we recommend:

  If you have gallstones, seek medical attention immediately.

Wegovy: Common (affecting up to 1 in 10 people).
Mounjaro: Uncommon (affecting fewer than 1 in 100 people).

• What is it?

  The medical term for changes in taste is ‘dysguesia’. Dysgeusia isn’t a serious medical condition, but it can impact your appetite.
  Common symptoms include:

  • A persistent metallic or bitter taste in all foods
  • Sweet or salty foods lose their usual flavor
  • Foods that once tasted good now seem unpleasant
  • A lingering bad taste in the mouth, even without eating anything
• Why does it happen?

  GLP-1s may impact the brain region responsible for taste and reward, which could explain this side effect.

• Here’s what we recommend:
  • Change up your food choices by eating citrus fruits, vinegar, and pickles. Avoid very sweet or spicy foods.
  • Drink plenty of water to prevent a dry mouth
  • Switch from metal utensils to plastic or ceramic
  • Brush and floss your teeth regularly
  • Avoid smoking

Uncommon (affecting fewer than 1 in 100 people taking Mounjaro or Wegovy).

• What is it?

  Heart palpitations are the feeling that your heart is racing or beating very fast. You might notice a “fast pulse” at rest.

• Why does it happen?

  Heart palpitations can be caused by changes in blood sugar levels and dehydration, both of which can affect heart rhythm. In some cases, the medication may also indirectly stimulate the nervous system, leading to an increased heartbeat. They can be brief or last for a few minutes.

• Here’s what we recommend:
  • Monitor your resting heart rate, either manually or by using a smartwatch/fitness tracker, and note any episodes of palpitations (an unusual awareness of your heartbeat).
  • Reduce triggers by cutting back on or avoiding caffeine, alcohol, and smoking—all of which can raise heart rate.

Uncommon (affecting fewer than 1 in 100 people without type 2 diabetes taking Mounjaro or Wegovy). It’s more likely to affect people who have type 2 diabetes, particularly those taking other medications such as insulin that lower blood sugar levels.

• What is it?

  Hypoglycaemia is a condition where your blood sugar (glucose) levels drop below a healthy range (typically below 70 mg/dL).
  Common symptoms of low blood sugar include:

  • Feelings of hunger, dizziness, confusion, tiredness, or weakness
  • Mood changes such as anxiety or irritability
  • Sweating
  • Shaking
  • Tingling lips
  • Heart palpitations
  • Changes in vision including blurred vision
• Why does this happen?

  GLP-1s increase insulin release after eating, so combining them with other glucose-lowering drugs can sometimes push blood sugar too low.

• Here’s what we recommend:
  • Have something sugary straight away – like fruit juice, a fizzy drink, glucose tablets, or sweets to raise your blood sugar. Once you start feeling better, follow up with something longer-lasting, like a slice of bread or some biscuits, to help keep your blood sugar steady.

Recent research has shown that there is no link between GLP-1 medication use and increased thyroid cancer risk in humans. However, some early research has suggested that GLP-1 medications may carry a potential risk of thyroid C-cell tumours, including medullary thyroid carcinoma (MTC).

Current guidance is that patients with a personal or family history of any thyroid cancer (including MTC or Multiple Endocrine Neoplasia syndrome type 2 (MEN2)) should not be prescribed GLP-1 medications.

If your personal or family history of any of these conditions changes, stop taking your treatment immediately and inform your MedExpress prescriber.

When to seek urgent medical attention