Side effects

One week you might feel a little nauseous. The next week, you barely notice anything. Then, another week, you might feel bloated or unusually full.

This kind of fluctuation is very common when starting GLP-1 treatment.

These medications affect hormone signals that control hunger and digestion. As your body adjusts to those changes, symptoms can come and go rather than following a straight line.

Experiencing different weeks doesn't mean your body is "getting worse" at tolerating the medication. In many cases, it's simply part of the adjustment process.

When symptoms vary from week to week, it often means your body is adapting, not that something's wrong.

When you're taking a new medication and start feeling "off", it's natural to wonder whether it's the treatment or something unrelated.

Sometimes the timing can offer a clue.

Symptoms that appear within a day or two of your injection and ease fairly quickly are often linked to the medication itself. Symptoms that develop gradually, come with a fever, or behave like a typical cold or stomach bug are more likely to be an illness.

That said, everyone responds differently. If something doesn't feel quite right or you're unsure what you're experiencing, our clinical team is always here to help you work through it.

If you're feeling well, that's not something to worry about. Some people start GLP-1 treatment and experience very few symptoms. Often, it simply means your body is tolerating the medication well.

Some people have a bumpier first few weeks, while others move through the early stages with barely a ripple. Neither experience is better or worse; they're just different responses to the same medication. Side effects are most common when you first start treatment or increase your dose, and usually improve on their own over time.

Most of the common side effects people notice with GLP-1 treatment involve the digestive system.

Because these medications slow down digestion, it's normal to experience things like nausea, bloating, wind, or going to the toilet less often than usual. These symptoms can feel uncomfortable, but they are a known and expected part of how the medication works.

What's not expected are symptoms like severe stomach pain, persistent vomiting, or anything that feels intense or worsening.

If you ever notice symptoms that feel very different from the usual adjustment effects, it's always worth seeking medical advice.

Dysesthesia is an unusual or uncomfortable skin feeling. People often describe it as tingling, pins and needles, buzzing, or a mild burning sensation. It is not nerve damage, and most people recover fully. Some people may find it uncomfortable, but it usually settles over time.

Researchers do not yet fully understand the exact cause. Wegovy acts on parts of the body that affect nerve signals. In some people, this can change how they feel nerve signals, which may lead to unusual skin sensations. Researchers are continuing to study this, as there is not yet one clear cause.

• Avoid tight clothing, heat, friction, or pressure on the skin, as these can make sensations worse.
• Moisturise regularly using emollients to keep skin comfortable.
• Use a warm or cold compress for short periods to ease discomfort.
• Stay well-hydrated and eat regularly, as dehydration or low electrolytes can worsen symptoms.
• Prioritise good-quality sleep, as poor sleep can make sensations feel stronger.
• Manage stress and anxiety, as worry can make skin sensations more noticeable.

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'.

Your GLP-1 treatments work 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.

• 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.

Your GLP-1 treatments work 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.

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.

• 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.

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.

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

• 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

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.

Your GLP-1 treatments can cause constipation due to slowing down the movement of food and waste through your digestive system.

• 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.

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.

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.

• 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

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.

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

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

A small dot of blood, a temporary raised lump, or mild bruising after injecting are all common and harmless. They don't mean anything went wrong or that your dose wasn't delivered.

Make sure you're correctly following the injection instructions.

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

• 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

Dysesthesia is an unusual or uncomfortable skin feeling. People often describe it as tingling, pins and needles, buzzing, or a mild burning sensation. It is not nerve damage, and most people recover fully. Some people may find it uncomfortable, but it usually settles over time.

Researchers do not yet fully understand the exact cause. Wegovy acts on parts of the body that affect nerve signals. In some people, this can change how they feel nerve signals, which may lead to unusual skin sensations. Researchers are continuing to study this, as there is not yet one clear cause.

• Avoid tight clothing, heat, friction, or pressure on the skin, as these can make sensations worse.
• Moisturise regularly using emollients to keep skin comfortable.
• Use a warm or cold compress for short periods to ease discomfort.
• Stay well-hydrated and eat regularly, as dehydration or low electrolytes can worsen symptoms.
• Prioritise good-quality sleep, as poor sleep can make sensations feel stronger.
• Manage stress and anxiety, as worry can make skin sensations more noticeable.

• 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 can help support your energy and digestion while your body adjusts.

Feeling unusually tired in the early weeks of GLP-1 treatment is something that lots of people mention.

Often, it isn't the medication itself causing the tiredness. It's the sudden change in how much you're eating. GLP-1 medications can reduce appetite quite quickly, and some people end up eating far less than they realise. When your body suddenly has less fuel, tiredness can follow.

In many cases, fatigue is simply a signal that your body needs more nourishment rather than less medication.

Making sure your meals include enough protein and nutrients can help support your energy levels while your body adjusts.

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

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

• 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

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.

Your GLP-1 treatments slow 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.

• 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

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.

Your GLP-1 treatments slow 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.

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

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

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

• 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

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.

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.

• 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.

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.

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.

If you have gallstones, seek medical attention immediately.

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

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

• 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

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

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.

• 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.

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.

Many people taking GLP-1 medication are also taking other prescriptions or managing existing health conditions. For most people, this is completely safe.

Before prescribing treatment, clinicians carefully review your medical history and any medications you're already taking. This helps make sure everything works safely together.

If anything changes while you're on treatment (such as starting a new medication or stopping one), it's important to let the clinical team know.

Keeping us informed helps us make sure your treatment continues to work safely and effectively for you.