What Supplements Should You Take on a GLP-1 Medicine?

On a GLP-1 medicine the supplements worth considering are the ones that stand in for what a smaller appetite no longer supplies: protein, fibre, electrolytes on sick days and magnesium, with vitamin D, vitamin B12, iron and folate as the nutrients to ask your GP to test rather than guess at. In one manufacturer-funded trial of 30 adults, semaglutide cut food intake by about a quarter, and a quarter less food carries a quarter less of everything in it unless the plate changes.¹ Nothing here replaces the medicine or adds to its effect; the question is nutritional, and food answers most of it.

• Protein first: the nutrient a small appetite drops furthest, and the one that protects muscle
• Fibre: 30 g a day is the UK target; the average UK adult manages about 20 g
• Test, don't guess: vitamin D, B12, ferritin and folate after months of eating less

Sources checked on 29 October 2026.

Why does a GLP-1 medicine change what you need from supplements?

The medicines copy the gut hormone GLP-1, hold its receptors stimulated all week, slow stomach emptying and quieten appetite.¹ Nobody plans to eat a quarter less protein, fibre or magnesium, but that is what happens when every portion shrinks and the bulky foods go first. Weight that comes off quickly includes muscle unless protein and resistance training protect it: in the tirzepatide body-composition sub-study about a quarter of the weight lost was lean mass.^{2, 3} This page is one chapter of our guide to living well on Mounjaro.

Do you need a protein supplement on a GLP-1 medicine?

Often, in the first months, because protein is the hardest target to hit on a small plate. The UK reference nutrient intake for adults is 0.75 g per kilogram of body weight a day, about 55 g for a man and 45 g for a woman.⁴ During deliberate weight loss the trials that protected muscle best used 1.2 to 1.6 g per kilogram, in portions of 25 to 30 g at each meal.⁵ Food first: eggs, Greek yoghurt, cottage cheese, chicken, fish, tofu, lentils and milk. A shake fits the meal you cannot face on a nauseous morning. Protein contributes to growth in muscle mass and to the maintenance of muscle mass, and a powder's label states its grams per serving.

Should you take a fibre supplement on a GLP-1 medicine?

If food cannot get you to 30 g a day, yes, slowly. The UK target is 30 g and the average adult manages about 20 g; a smaller appetite drops it further, because vegetables, pulses and wholegrains leave the plate first.^{4, 6} Fibre keeps stools soft when the gut is moving slowly, which matters because tirzepatide's product information lists constipation as very common, more than one person in ten, in its weight-management trials, and it extends fullness between small meals.¹² Oats, chia, pulses, pears and seeded bread come first; a supplement is a top-up, not a swap, and pace matters more than type: build up gradually and drink plenty of fluid, because fibre without water makes constipation worse.⁶ How much fibre you need on Mounjaro has the food list and the build-up plan.

Do you need electrolytes on a GLP-1 medicine?

On ordinary days, no: food and water supply the sodium, potassium and magnesium your body runs on. The days that change the answer are the ones with vomiting or diarrhoea, which lose fluid and salts together, or hot weather. The UK reference intake for potassium is 3,500 mg a day.⁴ A banana and a glass of milk for potassium, a pinch of salt in soup, nuts and seeds for magnesium fix most of it; an electrolyte sachet is the sick-day tool and never a reason to drink less water. A sachet's label states its sodium, potassium and magnesium, and magnesium contributes to electrolyte balance. Ask your pharmacist first if you take a blood-pressure medicine or have a kidney condition.

Is magnesium worth taking on a GLP-1 medicine?

The UK reference intake is 300 mg a day for men and 270 mg for women, and magnesium lives in nuts, seeds, wholegrains, pulses and leafy greens, exactly the foods a narrowed diet squeezes out.⁷ Magnesium contributes to the reduction of tiredness and fatigue and to normal muscle function. Read the elemental magnesium on the label and do not exceed the stated dose; more than 400 mg a day from supplements can cause diarrhoea, worth knowing on a medicine that already causes it.^{7, 12}

Which vitamins should you ask your GP to test?

Vitamin D, vitamin B12, ferritin and folate, with a full blood count, after a few months of eating less, or sooner if you are tired, breathless or shedding hair.¹⁰ Test rather than guess, because each shortfall looks like the medicine's own tiredness.

• Vitamin D. The NHS advises every adult to consider 10 micrograms a day from October to March, and not to exceed 100 micrograms a day from supplements.⁸ Vitamin D contributes to the maintenance of normal bones and to normal muscle function.
• Vitamin B12. The reference intake is 1.5 micrograms a day from animal or fortified foods, so it matters if meat, fish, eggs and dairy have dropped out, if you are vegan, or if you take metformin, which lowers B12 over years of use.^{4, 9} Vitamin B12 contributes to the reduction of tiredness and fatigue and to normal red blood cell formation.
• Iron and folate. Iron is the one never to take just in case: more than 20 mg a day commonly causes constipation, nausea and stomach pain, and very high doses can be fatal, particularly for children, so a ferritin test decides it.¹³ Folate comes from leafy greens and pulses.

The sub-hub which vitamins to take on Mounjaro goes nutrient by nutrient, including calcium and zinc.

Is there a best all-in-one supplement for a GLP-1 medicine?

No single product covers the list, because the list is mostly food: protein by the hundred grams and fibre by the tens of grams do not fit in a capsule, and a multivitamin supplies neither. Do GLP-1 supplements work covers the products sold as GLP-1 boosters, a different category.

What should you not take, or space from a GLP-1 medicine?

No vitamin or mineral is banned because of the medicine, but the slowed stomach changes timing: anything you swallow can be absorbed later or less completely, and the NHS advice is to tell your prescriber about every supplement and herbal remedy you take.¹¹ Four rules. Take psyllium and other bulk fibres at a different time from medicines, because the gel can slow their absorption. Take iron and calcium at different times from each other. Do not add iron, vitamin A above the reference intake or high-dose biotin without a reason, and tell whoever takes your blood about any biotin supplement, because it can distort thyroid and other test results.¹⁴ And treat berberine as a prescriber conversation, not a GLP-1 add-on: berberine with or after Mounjaro explains why. Tirzepatide, semaglutide and liraglutide are medicines, so a suspected side effect of the medicine goes to the MHRA Yellow Card scheme; a food supplement is not covered by Yellow Card, so report a reaction to it to your local authority's food safety team, which works with the Food Standards Agency.¹⁵

What we don't know

No trial has given a protein, fibre, magnesium or multivitamin supplement to people on a GLP-1 medicine and measured an outcome; the case for each rests on intake and the nutrient's authorised claims. No study has measured whether the slowed stomach changes vitamin and mineral absorption; the product information documents the effect for oral medicines only.¹² No trial has measured B12 absorption on tirzepatide; the medicine known to lower B12 is metformin.⁹

Frequently asked questions

What supplements should you not take while on a GLP-1 medicine?

None is forbidden, but iron without a test, vitamin A above the reference intake, high-dose biotin before a blood test, and anything claiming to copy the medicine are the ones to leave out. Tell your prescriber what you take.¹¹

Which GLP-1 companion supplement is the best?

The one that fills your own gap: for most people protein, then fibre, then an electrolyte sachet kept for sick days. A test decides the vitamins.

Does magnesium make you hungry?

No trial shows that. Magnesium contributes to normal muscle function and to the reduction of tiredness and fatigue; it has no measured effect on appetite in either direction.

Is the advice the same on Wegovy, Ozempic and Saxenda?

Yes. Semaglutide and liraglutide reduce intake and slow the stomach the same way, so the nutrition is the same.

Sources

1. Blundell J, et al. Effects of once-weekly semaglutide on appetite, energy intake, control of eating, food preference and body weight in subjects with obesity. Diabetes, Obesity and Metabolism, 2017. Randomised crossover trial, 30 adults, 12 weeks; manufacturer-funded. PubMed 28266779.
2. Look M, et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight. Diabetes, Obesity and Metabolism, 2025. Scan substudy of a randomised trial, 160 adults, 72 weeks; manufacturer-funded. PubMed 39996356.
3. Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine, 2022. Randomised trial (SURMOUNT-1), 2,539 adults, 72 weeks; manufacturer-funded. PubMed 35658024.
4. Public Health England. Government dietary recommendations: energy and nutrients, 2016; protein figures from COMA's 1991 Dietary Reference Values report (0.75 g per kilogram). Read 29 October 2026. assets.publishing.service.gov.uk.
5. Leidy HJ, et al. The role of protein in weight loss and maintenance. American Journal of Clinical Nutrition, 2015. Narrative review of meta-analyses and feeding trials; funding not stated on PubMed. PubMed 25926512.
6. NHS. How to get more fibre into your diet. Page last reviewed 2 March 2026. nhs.uk.
7. NHS. Vitamins and minerals: others, including magnesium and potassium. Page last reviewed 3 August 2020 (review overdue). nhs.uk.
8. NHS. Vitamin D. Page last reviewed 3 August 2020 (review overdue). nhs.uk.
9. de Jager J, et al. Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. BMJ, 2010. Randomised placebo-controlled trial, 390 adults, 4.3 years; funding not stated on PubMed. PubMed 20488910.
10. NHS. Iron deficiency anaemia. Page last reviewed 26 January 2024. nhs.uk.
11. NHS. Tirzepatide. Page last reviewed 15 May 2026. nhs.uk/medicines/tirzepatide.
12. Tirzepatide Summary of Product Characteristics, sections 4.5 and 4.8, electronic medicines compendium, date of revision of the text 29 August 2026. medicines.org.uk.
13. NHS. Vitamins and minerals: iron. Page last reviewed 3 August 2020 (review overdue). nhs.uk.
14. Li D, et al. Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults. JAMA, 2017. Non-randomised crossover study, 6 adults, 7 days; US government funding, authors report diagnostics-company fees. PubMed 28973622.
15. Food Standards Agency. How to report a food safety or hygiene issue for members of the public. Updated 5 August 2026. gov.uk.

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.

This article is general information, not medical advice. Mounjaro, Wegovy, Ozempic and Saxenda are prescription medicines: follow your prescriber's instructions and speak to your prescriber or pharmacist before adding any supplement.