Which Vitamins to Take on Mounjaro? What Helps and What to Avoid

What vitamins should I take on Mounjaro?

On Mounjaro (tirzepatide), take 10 micrograms of vitamin D a day from October to March, as the NHS advises every adult in the UK, and add vitamin B12, iron, calcium or a multivitamin when your plate has narrowed or a blood test shows a gap.^{1, 5} The medicine slows the stomach, which its product information says can change how quickly an oral medicine is absorbed; no study has measured vitamin absorption on it, and what clearly changes is how much you eat.²⁰

Evidence at a glance

• Nutrient status on GLP-1 medicines: one 2026 review, 6 studies, 480,825 adults, mainly observational; vitamin D deficiency in 7.5% at six months and 13.6% at twelve; ferritin 26% to 30% lower than in a comparison group.²
• Body composition: in the manufacturer-funded 160-person substudy of the main tirzepatide trial, about a quarter of the weight lost was lean tissue, as with placebo.³
• Common side effects on the NHS list include feeling tired and hair loss, alongside the gut effects.¹
• Not tested: no trial has given a vitamin or mineral to people taking tirzepatide and measured whether it changed anything.

Sources checked on 17 October 2026.

This is the supplements chapter of living well on Mounjaro; the medicine-neutral version is what supplements to take on a GLP-1 medicine.

Does Mounjaro cause vitamin deficiency?

Not directly, on the evidence so far. The product information says tirzepatide delays stomach emptying and so may change the rate at which oral medicines are absorbed; no study has measured vitamin or mineral absorption, and the NHS lists no deficiency among its side effects.^{1, 20} What the medicine clearly does is cut appetite, so meals shrink and over months a smaller plate tends to become a narrower one.¹ In the 2026 review, vitamin D intake averaged about 20% of the recommended amount, more than 60% of users were below their requirements for calcium and iron, ferritin ran 26% to 30% lower than in people on a different class of diabetes medicine, and B12 deficits grew with time on treatment.² The studies were mainly observational, so they cannot prove the medicine caused the gaps; eating much less, of fewer foods, is the obvious route.²

Do I need to take vitamins on Mounjaro?

Vitamin D in autumn and winter, yes, because that advice is for every adult in the UK.⁵ Beyond that, a supplement earns its place when the food that carried a nutrient has gone: if you eat far less than you used to or skip meals, have dropped a whole food group, are vegan or vegetarian, take metformin, are older (B12 is harder to absorb with age), or have had bariatric surgery.^{10, 19} Symptoms overlap with the medicine's own tiredness, so a blood test is the only way to know: a full blood count, ferritin, B12, folate, vitamin D and thyroid function are the ones GPs use, and why am I so tired on Mounjaro walks through the medicine-or-under-eating check.

Which supplements are worth taking on Mounjaro?

Can you take vitamin D with Mounjaro?

Yes. The NHS advice to every adult applies: consider 10 micrograms (400 IU) a day from October to early March, all year if you are rarely outdoors, cover your skin or have dark skin, and no more than 100 micrograms (4,000 IU) a day.⁵ No interaction with tirzepatide is listed.¹ Vitamin D contributes to the maintenance of normal bones, the maintenance of normal muscle function and the normal function of the immune system.¹⁸ The vitamin D guide sets out D2, D3 and the plant sources with the trials behind each.

Does Mounjaro cause B12 deficiency?

Not in any study so far: no trial has measured B12 absorption on tirzepatide, and the medicine known to lower B12 is metformin.^{10, 20} In the Diabetes Prevention Program follow-up, 2,155 adults randomised to metformin or placebo, low or borderline B12 was found in 19.1% of the metformin group at five years against 9.5% on placebo.¹⁰ B12 comes from meat, fish, eggs, dairy and fortified foods, so months of eating far less of them is the other route; adults need about 1.5 micrograms a day.^{2, 19} Vitamin B12 contributes to normal red blood cell formation, normal functioning of the nervous system and the reduction of tiredness and fatigue.¹⁸ Tiredness, pins and needles or a sore tongue are among the NHS symptoms,⁹ and a B12 level is the test that shows whether they are a B12 question; signs of B12 deficiency lists the rest.

Mounjaro and iron deficiency

Iron is the one nutrient to test before you supplement. The NHS amounts are 14.8 mg a day for women aged 19 to 49 and 8.7 mg for men and for women over 50; more than 20 mg a day commonly causes constipation, nausea, vomiting and stomach pain.⁶ Iron contributes to normal formation of red blood cells and haemoglobin and to the reduction of tiredness and fatigue.¹⁸ Tiredness, breathlessness, palpitations and paler skin are the NHS symptoms of iron deficiency anaemia; a GP confirms it with a full blood count and ferritin.⁷ Iron supplement side effects covers the rest.

Can you take magnesium with Mounjaro?

Yes. No interaction between magnesium and tirzepatide is documented and no trial has tested the two together; the NHS names other diabetes medicines and warfarin as the ones that may not mix well, and asks you to tell a doctor or pharmacist about any vitamins or supplements you take.¹ Adults need 300 mg a day (men) or 270 mg (women), from nuts, seeds, wholegrains and leafy greens; more than 400 mg a day from supplements is likely to cause diarrhoea.¹¹ Magnesium contributes to normal muscle function, normal functioning of the nervous system, normal psychological function and the reduction of tiredness and fatigue.¹⁸

Calcium, zinc and potassium

Calcium: adults need 700 mg a day, most of it from dairy or fortified plant milk, and the 2026 review recorded more than 60% of users below that.^{2, 12} Calcium is needed for the maintenance of normal bones;¹⁸ do you need a calcium supplement works through the decision. Zinc: 9.5 mg (men) or 7 mg (women) a day, from meat, shellfish, pulses and seeds;¹¹ zinc contributes to the normal function of the immune system and to the maintenance of normal skin,¹⁸. Potassium, sodium and fluid matter most when vomiting or diarrhoea are part of the picture; older people should not take potassium supplements unless a doctor advises it,¹¹ and do you need electrolytes on Mounjaro covers it.

Protein and fibre

Neither is a vitamin, and both fall with food volume. In the 160-person body-composition substudy of the main tirzepatide trial, six of whose eight authors were employees of the manufacturer, about a quarter of the weight lost was lean tissue, as with placebo, and a pooled analysis of 22 trials in 2,258 adults found the same share across GLP-1 medicines.^{3, 4} Does Mounjaro cause muscle loss and how much protein you need on Mounjaro set the targets; how much fibre you need on Mounjaro covers the constipation side.

What vitamins should you NOT take with Mounjaro?

No vitamin is dangerous purely because you take tirzepatide; the NHS interaction list is other diabetes medicines, warfarin, insulin and anaesthetics.¹ The cautions are about amounts and timing.

• Vitamin A above the NHS figure. Averaging more than 1.5 mg a day over many years may weaken bones, and the NHS says not to take supplements containing vitamin A, fish liver oil included, if you eat liver weekly.¹³ What vitamin A is good for covers retinol against beta-carotene.
• Iron without a result. Over 20 mg a day commonly means constipation and nausea, and iron accumulates; test first.⁶
• High-dose biotin in the week before a blood test. In a six-person crossover study, 10 mg of biotin a day for seven days skewed 9 of 23 biotin-based laboratory assays in a panel that included thyroid hormones and ferritin; tell whoever takes your blood.¹⁵
• Vitamin K if you take warfarin. Vitamin K contributes to normal blood clotting, and the NHS flags warfarin on the tirzepatide page too; check any vitamin D3 and K2 combination with your GP first.^{1, 14, 18}
• High-sodium electrolyte sachets if you manage blood pressure; the electrolytes page has the figures.
• Herbal remedies nobody knows about. The NHS says some herbal remedies and supplements may not mix well with tirzepatide; tell a doctor or pharmacist before you start one.¹

Stay within the NHS supplement figures across every product you take, and tell your GP or pharmacist about every supplement.¹¹

Do you need a multivitamin on Mounjaro?

A multivitamin covers several nutrients at around the reference intake each; no trial has given one to people on tirzepatide and measured an outcome, so the case rests on the 2026 review's finding that more than 60% of users ate below their calcium and iron requirements.² Read the vitamin A, iron and biotin lines, and take it with a small snack. "Best multivitamin for women on Mounjaro" has no trial answer; how to choose a multivitamin for women explains what a women's formula should contain at each age. And there is no tirzepatide gummy: tirzepatide is a prescription injection, and anything sold as a gummy under the medicine's name is a different product; do GLP-1 supplements work covers what those contain.¹

Can Mounjaro cause hair loss?

Yes: the NHS lists hair loss among tirzepatide's common side effects.¹ The usual mechanism is telogen effluvium, a diffuse shedding set off by a physiological shock such as sudden weight loss that usually remits, which is why the nutrients to secure are protein, iron, zinc and the B vitamins.¹⁶ Biotin contributes to the maintenance of normal hair, and zinc contributes to the maintenance of normal hair.¹⁸ Does Mounjaro cause hair loss has the timeline, does zinc help with hair loss the zinc trials, and should you take collagen on Mounjaro where collagen fits.

Every guide in this series

The hub is living well on Mounjaro. Eating: what to eat, the 7-day meal plan, what to avoid, alcohol and foods that raise your own GLP-1. Side effects: tiredness, hair loss, Mounjaro face, constipation and diarrhoea, sulphur burps, heartburn and how long side effects last. Women: side effects in women, the pill, HRT and menopause and pregnancy. Also: how Mounjaro works and what happens when you stop.

What we don't know

• No randomised trial has given a vitamin or mineral to people taking tirzepatide and measured deficiency, symptoms or weight.²
• Whether the delayed stomach emptying changes how much of a vitamin or mineral is absorbed, not only when; the product information covers oral medicines, not nutrients.²⁰
• Whether protein, a multivitamin or both reduce the hair shedding or the lean-tissue share.^{3, 16}

Frequently asked questions

Can you take magnesium glycinate or citrate on tirzepatide?

Yes, either. No interaction with tirzepatide is documented and no trial has tested the pair; the NHS asks only that a doctor or pharmacist knows what you take.¹ Glycinate (bisglycinate) and citrate both deliver magnesium; compare the label's elemental figure against the 400 mg a day the NHS says is unlikely to cause harm; above that, loose stools are likely.¹¹ What is magnesium glycinate and what is magnesium citrate cover each form; neither is ranked above the other.

Can you take lion's mane or ashwagandha with tirzepatide?

No study has tested either with tirzepatide. The NHS says some herbal remedies and supplements may not mix well with it, and its herbal-medicines page puts diabetes medicines among those that do not mix well with herbal products.^{1, 17} Neither herb has a UK authorised health claim.¹⁸ Lion's mane side effects records animal glucose data and no human trial with diabetes medicines; what you can take with ashwagandha carries the NHS list.

Can tirzepatide cause anaemia?

Anaemia is not among the side effects the NHS lists for tirzepatide; feeling tired is.¹ Eating much less meat, fish, eggs, dairy and fortified cereal for months can lower iron, B12 and folate, and the 2026 review did record lower ferritin and rising B12 deficits.² Iron contributes to normal formation of red blood cells and haemoglobin and vitamin B12 to normal red blood cell formation; neither is a reason to take iron without a result.¹⁸

Should you take a probiotic on tirzepatide?

No trial has tested live cultures in people taking tirzepatide, so there is no evidence that picks one out, and no live-culture product carries a UK authorised health claim.¹⁸ The NHS asks you to tell a doctor or pharmacist about any supplement alongside tirzepatide.¹ If you already take a live-culture product and it suits you, nothing about tirzepatide changes that; what are probiotics sets out the trials in which live cultures were tested, and for whom.

Do you need B12 injections on tirzepatide?

Only if a blood test shows a deficiency with a cause that tablets cannot fix, and a GP decides. No study has measured B12 absorption on tirzepatide; the risk is months of eating far less animal food.²⁰ The NHS treats B12 deficiency anaemia with hydroxocobalamin injections when the cause is not dietary, "every 2 to 3 months for the rest of your life" in pernicious anaemia, and with daily tablets, or an injection twice a year, when diet is the cause.⁸ That pathway is for confirmed deficiency; none of the studies cited here gave B12 injections to people with normal levels and measured energy or weight. Vitamin B12 contributes to the reduction of tiredness and fatigue, and a test shows whether yours is a B12 question.^{8, 18}

Sources

1. NHS. Tirzepatide. Reviewed 15 May 2026. nhs.uk.
2. Urbina J, et al. Micronutrient and nutritional deficiencies associated with GLP-1 receptor agonist therapy: a narrative review. Clinical Obesity, 2026. Narrative review, 6 studies, 480,825 adults, mainly observational; no funding or conflicts listed on PubMed. PubMed 41549912.
3. 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.
4. Karakasis P, et al. Effect of GLP-1 receptor agonists and co-agonists on body composition: systematic review and network meta-analysis. Metabolism, 2025. Pooled analysis, 22 randomised trials, 2,258 adults; authors declare industry fees. PubMed 39719170.
5. NHS. Vitamin D. Reviewed 3 August 2020. nhs.uk.
6. NHS. Vitamins and minerals: iron. Reviewed 3 August 2020. nhs.uk.
7. NHS. Iron deficiency anaemia. Reviewed 26 January 2024. nhs.uk.
8. NHS. Vitamin B12 or folate deficiency anaemia: treatment. Reviewed 20 February 2023 (review overdue). nhs.uk.
9. NHS. Vitamin B12 or folate deficiency anaemia: symptoms. Reviewed 20 February 2023 (review overdue). nhs.uk.
10. Aroda VR, et al. Long-term metformin use and vitamin B12 deficiency in the Diabetes Prevention Program Outcomes Study. Journal of Clinical Endocrinology and Metabolism, 2016. Follow-up of a randomised trial, 2,155 adults, 5 and 13 years; US government funding. PubMed 26900641.
11. NHS. Vitamins and minerals: others (magnesium, potassium, zinc). Reviewed 3 August 2020. nhs.uk.
12. NHS. Vitamins and minerals: calcium. Reviewed 3 August 2020. nhs.uk.
13. NHS. Vitamins and minerals: vitamin A. Reviewed 3 August 2020. nhs.uk.
14. NHS. Vitamins and minerals: vitamin K. Reviewed 3 August 2020. nhs.uk.
15. 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.
16. Chien Yin GO, et al. Telogen effluvium: a review of the science and current obstacles. Journal of Dermatological Science, 2021. Narrative review; no funding or conflicts listed on PubMed. PubMed 33541773.
17. NHS. Herbal medicines and complementary therapies. Reviewed 1 May 2026. nhs.uk.
18. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register, last updated 19 May 2026. gov.uk.
19. NHS. Vitamins and minerals: B vitamins and folic acid. Reviewed 3 August 2020. nhs.uk.
20. Tirzepatide Summary of Product Characteristics, section 4.5 (interactions), electronic medicines compendium, date of revision of the text 29 August 2026. medicines.org.uk.

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General information, not personal medical advice. Mounjaro is a prescription medicine: follow your prescriber's instructions, and speak to your GP or pharmacist before starting a supplement if you take other medicines or have a health condition.