Managing side effects with diet
Dietary advice for people taking weight loss medicines
Side effects can be more intense during your first 6 months of taking weight loss medicines.
Your side effects might feel worse immediately after getting another dose. They usually settle after your body gets used to the medicine.
Adjusting your diet can help with your side effects.
Constipation
Weight loss medicines slow down digestion. This helps you to feel fuller for longer but it can also cause constipation.
You might drink less water or eat less fibre while on weight loss medicines because you feel less hungry. This can also cause constipation.
Do
- drink 2 litres of water or low-calorie drinks throughout the day
- add 1 tablespoon of chia seeds or flax seeds to your meals
- eat more fibre including fruits, vegetables and wholegrain carbohydrates like brown rice
- add lentils, chickpeas, beans or peas into your meals
- try eating 1 to 2 kiwi fruit a day
- eat a handful of prunes, figs, raisins or dried apricots as a snack
- move your body, especially in the morning – even a short walk can help
Diarrhoea
Weight loss medicines can cause diarrhoea. Usually this gets better after your body adjusts to the medicine.
You lose a lot of fluids when you have diarrhoea so it's important to stay hydrated.
Do
- drink lots of low-calorie fluids
- eat small meals more frequently
- eat more fibre including fruits, vegetables and wholegrain carbohydrates like brown rice
Tiredness and headaches
Feeling tired and getting headaches is a common side effect.
Do
- drink at least 2 litres of water or low-calorie drinks throughout the day
- eat small meals more frequently – avoid skipping meals
- take time to rest when you can
- use hot or cold compresses on your head and neck
- get plenty of fresh air
- consider taking a daily A-to-Z multivitamin and mineral supplement
Feeling sick, heartburn and vomiting
Weight loss medicines slow the movement of food and fluid through your gut. This can make you feel sick (nausea), get heartburn or be sick (vomit).
These side effects usually go away within 3 to 4 weeks of starting or increasing your dose.
Do
- eat small meals more frequently
- eat bland and dry foods like crackers
- drink 2 litres of water or low-calorie drinks throughout the day
- drink ginger, peppermint or fennel tea
- try cold foods instead of hot foods
- get plenty of fresh air
- distract yourself by reading, watching a film or listening to music
Don't
- do not eat fatty foods
- do not eat or cook strong-smelling foods
- do not lie down soon after eating
Foods to try when you’re feeling sick
Eating plain foods can help you feel better.
You can eat plain carbohydrates such as:
- plain crackers, breadsticks or dry toast
- plain porridge
- boiled or mashed potatoes
- plain rice or pasta
Or plain proteins such as:
- boiled or scrambled eggs
- cheddar cheese
- cottage cheese
- cold, sliced meats
- plain Greek yoghurt
- soft tofu
- nuts and seeds
Some fruits and vegetables can be soothing, like:
- bananas
- cucumber
- melon
- steamed carrots, courgette or squash
When to get help
Most side effects get better after you body gets used to the medicine. If your side effects get worse, contact a GP or your care team.
Contact your healthcare team or a GP if:
- you are vomiting more than 3 times a day
- you cannot keep down fluids
- your pee turns a dark colour
- you feel lightheaded
The medicine might not be suitable for you or you may be dehydrated.
Resource number: 5545/VER1
Last reviewed: August 2025
Next review due: August 2028
