Managing side effects of GLP-1 injections for weight loss

How effective are GLP-1 weight loss injection medicines?

Wegovy 

Clinical trials have demonstrated that participants (individuals with a BMI of 30+, or individuals with a BMI of 27+ and a high-risk, weight-related health condition such as high blood pressure) given 2.4mg of semaglutide once a week lost approximately 12-15% of their starting body weight over a 68-week trial period on average, compared with participants given a placebo drug (no active ingredient) who lost approximately 2.5% of their starting body weight in the same timeframe. Both participant groups also engaged in regular physical activity and a calorie-controlled diet. The clinical trial involved 1,961 adults in total, and you can read the full details of the study in this New England Journal of Medicine publication.     

Mounjaro 

A clinical trial to assess the effectiveness of tirzepatide (the active ingredient in Mounjaro) in treating obesity demonstrated an average weight loss of 15-22% over 72 weeks in participants who received the ‘live drug’ rather than the placebo. Participants receiving the placebo, by comparison, lost approximately 3% of their body weight in the same period, with both groups following a calorie-controlled diet and engaging in regular physical activity throughout. The full results of this study are also published in the New England Journal of Medicine.  

These studies show promising results in the effectiveness of both Wegovy and Mounjaro in supporting adults with obesity to reach a healthy body weight. If you’ve been prescribed one of these weight loss injections, or you’re considering speaking to a healthcare provider about whether either Wegovy or Mounjaro might be suitable for you, it’s important to be aware of possible side effects and how you can manage common symptoms if you experience them.  

What are the possible side effects of GLP-1 injections?

Whether you experience side effects when using GLP-1 injections depends on which medication you use and how your body responds to it. As with all medicines, GLP-1 injections can cause side effects, although most of these are mild and generally improve within a few weeks.

You begin GLP-1 injections on a low dose and gradually increase it. A doctor will regularly assess how your body is tolerating it.

When to seek medical advice

Some rare side effects are more serious. If you start feeling extremely weak, tired or dizzy, have severe stomach pain, hair loss, a fast heartbeat or an allergic reaction, it is important to talk to a doctor immediately.

Recognising common GLP-1 side effects

Side effects of GLP-1 injections often affect digestive health. There are ways to take control of your symptoms so you can start feeling like you again.

Constipation

GLP-1 injections may slow down bowel movements, leading to constipation. This can cause discomfort and digestive issues if not managed properly.

Things you can do to gently relieve constipation:

• Drink plenty of fluids throughout the day.

• Exercise regularly.

• Increase your fibre intake by eating more fruits, vegetables and whole grains.

• Eat the recommended 30 grams of fibre a day. This can be challenging if you’re not feeling hungry. Try adding fibre sachets, psyllium husk or inulin to your diet.

Pharmacy treatments can help get things moving. Explore options for constipation relief.

Bloating, burping and wind

GLP-1 injections slow down the speed that food leaves your stomach which makes you feel fuller for longer. When food lingers in the stomach and intestines (digestive tract), there is more time for it to be fermented by the gut bacteria. This can lead to an increase in gas causing bloating, wind and the need to burp. The higher the dose of GLP-1 injection, the higher the likelihood of symptoms while your body gets used to it.

While bloating, burping and wind often calm down, there are ways to ease digestion and lessen discomfort:

• Stay hydrated by drinking water. Avoid using a straw or drinking fizzy drinks as these add extra gas to your digestive tract.

• Eat small, regular meals, to ease pressure in your stomach.

• Chew food thoroughly and eat slowly to prevent swallowing too much air.

• Choose low-fat foods and lean protein, like chicken, fish, eggs and tofu. (High-fat foods take longer to digest).

• Avoid acidic or spicy foods that can irritate your stomach.

• Keep moving. Go for a gentle walk and avoid lying down after eating.

It is important to support your gut health. Consume probiotic foods (such as kefir, kimchi, sauerkraut and yogurts that contain probiotic cultures) and prebiotic foods (such as fruits, vegetables, legumes and grains) to help your gut bacteria thrive. Or take probiotic supplements.

Indigestion, heartburn and reflux

Keeping the stomach full for longer and slowing digestion means that GLP-1 injections can cause indigestion, or the burning sensation of heartburn and reflux. These symptoms often settle with time, but there are ways to soothe them:

• Eat slow, small, frequent meals to put less pressure on your stomach. 

• Watch out for common triggers, like acidic (citrus fruits, vinegar), high-fat (fried, rich, greasy) and spicy foods.

• Look after your gut by eating probiotics (some natural yogurt, kefir, kimchi) and prebiotics, (fruits, vegetables, legumes and grains), or taking probiotic supplements.

• Drink water to stay hydrated. Avoid caffeinated and fizzy drinks that can irritate your digestion.

• Go for a gentle walk and avoid lying down after eating.

• Wear comfortable clothing.

• Stress can worsen digestive issues. Practice breathing exercises or meditation.

• Raise your head with an extra pillow to help relieve reflux when sleeping.

• If you smoke, nicotine can make reflux worse. Read inspiration and advice to help you quit for good.

Pharmacy treatments can help calm digestion. Explore pharmacy options for indigestion, heartburn and reflux relief.

Diarrhoea and loose stools

GLP-1 injections can cause diarrhoea or loose stools because digestion slows down. They can alter how fluid is absorbed in the gut.

Diarrhoea commonly happens after GLP-1 injections have started or a dose has been increased, but it should improve. There are ways to cope at home as your body adjusts to the medicine:

• Keep hydrated, sip water throughout the day.

• Eat bland, low-fat foods like rice, pasta, bananas and toast to settle your stomach.

• Replace lost electrolytes with diluted, low sugar sports drinks or Dioralyte.

• Take care of your gut bacteria with probiotic supplements.

Pharmacy treatments can help protect the digestive tract or stop the diarrhoea. Explore options for diarrhoea relief.

Nausea and sickness

Feeling and being sick are very common side effects of GLP-1 injections because of the effect on digestion and signals in the brain. To calm nausea and sickness:  

• Go for a gentle walk to get fresh air.

• Stick to plain foods or try products that contain ginger, like a ginger biscuit.

• Sip on water or peppermint tea.

• Replace lost electrolytes with diluted, low sugar sports drinks or Dioralyte.

• Wear comfortable clothing.

• Care for your gut bacteria with probiotic supplements.

• Pharmacy treatments can help settle sickness. Explore pharmacy treatment options for nausea and sickness relief.

Headache

Headaches are a very common side effect of GLP-1 injections and could be caused by dehydration or lowering blood sugar levels. Things you can do to relieve your headaches:

• Keep sipping on water and stay hydrated.

• Get some fresh air.

• Avoid screens or brightly lit areas.

• Pharmacy treatments can help soothe your pain. Explore options for headache relief.

Dry mouth or changes in taste

The GLP-1 medicine can interact with taste buds on the tongue, so you may notice a change in taste. You might also experience a dry mouth due to changes in saliva production or dehydration.

Tips to try:

• Regularly sip on water and have some nearby at bedtime.

• Drink water with meals to help with chewing and swallowing.

• Avoid fizzy drinks and those containing caffeine, alcohol and sugar as these can make you thirsty.

• Stimulate saliva by chewing sugar-free gum or sucking on a hard sweet.

• Keep up your oral hygiene – brush and floss your teeth regularly and use an alcohol-free mouthwash.

• Pharmacy treatments can help keep your mouth feeling fresh. Explore options for dry mouth relief.

Feeling weak or tired

The weight management journey with GLP-1 injections sometimes makes people feel low in energy. Even though you have less appetite, you need to get enough essential nutrients to fuel your body. Skipping meals could cause your energy to crash due to blood sugar dips.

Help boost your energy and digestion:

• Sip on water throughout the day.

• Eat small, regular, nutritious meals.

• Manage any energy-draining side effects like nausea, vomiting, and diarrhoea.

• Get into good sleep habits with a relaxing, screen-free bedtime for good-quality sleep.

• Do gentle movement and short walks.

• If you start feeling very weak, tired, or dizzy, you must talk to a doctor.

Pharmacy treatments can help support your health and wellbeing. Explore the Pharmacy2U Health & Wellness Shop.

The rarer, but more serious side effects of GLP-1 injections

Both active ingredients in Wegovy and Mounjaro are known as glucagon-like peptide-1 receptor agonists (GLP-1 RAs). This essentially means that they mirror the action performed by our bodies’ GLP-1 hormone, which is released in the stomach when we eat. This hormone helps regulate how much we eat by sending signals to the brain about our fullness levels. This can help reduce appetite and result in weight loss. As with all medicines, both semaglutide and tirzepatide can cause side effects, although the majority of these are usually mild and temporary. However, there are some serious side effects that, although rare, are worth knowing about so you can spot the signs and take immediate action if you suspect them.  

Acute pancreatitis  

This refers to sudden inflammation of the pancreas and, in rare cases, has been linked to the use of weight loss injections. It’s characterised by the sudden onset of severe tummy pain that can move into the back area. Other symptoms include a high temperature (38°C+), nausea and vomiting, indigestion, a yellow tinge to the skin and whites of the eyes (jaundice), a swollen or tender stomach, and a rapid heartbeat.  

If you suspect you may have developed acute pancreatitis, stop using your weight loss medication and contact your prescribing doctor straight away. If this isn’t possible, contact NHS 111.   

Gallbladder issues 

The gallbladder is a small organ that stores bile produced by the liver. Gallstones are a primary gallbladder issue that can cause acute pancreatitis. They are small deposits of cholesterol, and while they don’t usually have symptoms, if they travel to an opening in the gallbladder, they can cause a blockage that leads to intense stomach pain lasting between 1-5 hours. They can sometimes cause complications, including an inflamed gallbladder (known as gallstone disease). This inflammation can cause similar symptoms to acute pancreatitis. Seek medical advice straight away if you develop any of these.   

Low blood sugar 

This side effect is more likely if you have type 2 diabetes. You might notice you feel dizzy or lightheaded if you develop low blood sugar. It can be a good idea to invest in an at-home blood sugar (glucose) monitor if you’re starting Wegovy or Mounjaro, so you can check your levels regularly. Your glucose levels should be at or above 4mmol/L. Other symptoms of low blood sugar include blurred vision, anxiety, feeling shaky, drowsy, or weak, developing slurred speech, a headache, or a rapid heart rate. If you notice these symptoms, eat or drink something sugary to boost your glucose levels and take a blood sugar reading after 10-15 minutes. Contact your prescribing clinician or visit NHS 111 online if you’re concerned.  

Kidney problems 

If you have an existing kidney issue, typical side effects of weight loss injections, such as diarrhoea and vomiting, can lead to dehydration, which can aggravate and worsen existing kidney conditions. To avoid this, please make sure you drink plenty of fluids regularly throughout the day.  

Severe allergic reaction (anaphylaxis) 

In rare cases, Wegovy and Mounjaro may cause severe allergic reactions in some people. If you notice symptoms including swelling around the lips, tongue, throat, or face, difficulty breathing or swallowing, a significant increase in heart rate, fainting or dizziness, or a sudden rash and intense itching, seek immediate medical attention.  

Struggling with GLP-1 injections side effects?

If you are worried by any side effects, or they do not improve, or if they start to affect your daily life, speak with a doctor or pharmacist for help and advice.

Where to report side effects

If you experience side effects of any medicine, please report these via the Yellow Card Scheme. The Yellow Card Scheme is operated by the Medicines and Healthcare Products Regulatory Agency (MHRA) and helps to continuously monitor the safety of medicines and healthcare products.

You can access the Yellow Card Scheme either through the reporting website or by downloading the MHRA app.

This information is for educational purposes and does not replace professional medical advice. Always consult your doctor or pharmacist for personalised advice.