Multivitamins and Mounjaro: do you need one?

In short

GLP-1 medicines cut energy intake by 16% to 39%, according to a review cited in NHS prescribing guidance
The NHS advises everyone to consider 10 micrograms (400 IU) of vitamin D a day from October to early March
Women aged 19 to 49 need 14.8mg of iron a day and men need 8.7mg
Adults need about 1.5 micrograms of vitamin B12 and 200 micrograms of folate a day
If you might get pregnant, the NHS advises 400 micrograms of folic acid a day. Mounjaro must be stopped at least 1 month before trying to conceive
Iron supplements of 17mg a day or less are unlikely to cause harm. Doses over 20mg can cause nausea and constipation

Most people on Mounjaro do not need a prescription supplement, but a basic multivitamin is a sensible safety net if you eat much less than before. Smaller meals mean less iron, vitamin B12, folate and vitamin D coming in. Some NHS guidance for GLP-1 treatment suggests a standard once-a-day A to Z multivitamin and mineral supplement. Everyone in the UK should consider 10 micrograms of vitamin D a day from October to early March.

Why eating less raises the risk of a gap

Mounjaro works by reducing appetite. A review cited in NHS prescribing guidance from Bath and North East Somerset, Swindon and Wiltshire ICB found GLP-1 medicines cut energy intake by 16% to 39%. The same guidance warns this drop can leave people short of vitamins and minerals, and advises baseline blood tests with any deficiency corrected.

Three things make gaps more likely on Mounjaro:

Portions shrink, but your needs for iron, B12 and folate stay the same.
Meat, eggs and rich foods can become unappealing, and these carry much of the iron and B12 in a typical UK diet.
Vomiting or diarrhoea in the early weeks can mean less food is absorbed or kept down.

A supplement fills gaps. It does not replace food. Protein, fibre and energy come only from meals, and the guide to eating well on Mounjaro covers how to build them.

The nutrients to watch

Nutrient	Daily need for adults (NHS)	Main food sources	Signs of a shortfall
Iron	14.8mg for women 19 to 49, 8.7mg for men and women over 50	Red meat, beans, chickpeas, nuts, dried apricots, fortified cereals	Tiredness, shortness of breath, pale skin, noticeable heartbeats
Vitamin B12	About 1.5 micrograms	Meat, fish, milk, cheese, eggs, fortified cereals	Pins and needles, sore red tongue, mouth ulcers, memory problems
Folate	200 micrograms	Green vegetables, chickpeas, fortified cereals	Tiredness, mouth ulcers, low mood
Vitamin D	10 micrograms in autumn and winter	Oily fish, egg yolks, red meat, fortified spreads and cereals	Often none. Bone and muscle pain over time

Women who still have periods after 50 may need the higher iron figure. Calcium is worth a thought too. Dairy is the main UK source, and the NHS Eatwell Guide counts it as important for bones.

Iron

Iron is the nutrient most likely to run short in women of childbearing age, with or without Mounjaro. If you have heavy periods, eat little red meat, or follow a vegetarian or vegan diet, your risk is higher. Iron from plant foods is absorbed better when eaten with vitamin C, such as a glass of orange juice or peppers in a bean stew.

The NHS says taking 17mg or less of iron a day from supplements is unlikely to cause harm. Doses over 20mg can cause constipation, nausea, vomiting and stomach pain, which overlap with Mounjaro side effects. Do not take a high-dose iron tablet without a blood test showing you need one.

Vitamin B12

B12 comes almost only from animal foods. Vegans need a fortified food or a supplement whether or not they take Mounjaro. Many people on Mounjaro for type 2 diabetes also take metformin. The MHRA advised in 2022 that metformin can reduce B12 levels, and recommends testing B12 in people on metformin who have symptoms of deficiency.

Folate and pregnancy planning

Adults need 200 micrograms of folate a day from food. If you might get pregnant, the NHS advises a 400 microgram folic acid supplement every day, started before you stop contraception and continued until 12 weeks of pregnancy. The Mounjaro leaflet says not to use the medicine in pregnancy and to stop at least 1 month before you try to conceive. Folic acid should start around the same time. The page on Mounjaro and pregnancy covers planning in full.

Vitamin D

From October to early March, sunlight in the UK is too weak for your skin to make enough vitamin D. The NHS advises everyone to consider 10 micrograms (400 IU) a day in these months. People rarely outdoors, or who cover their skin when outside, should take it all year. The NHS warns not to take more than 100 micrograms (4,000 IU) a day.

Choosing a basic multivitamin

You do not need a special GLP-1 product. A standard supermarket or pharmacy own-label A to Z multivitamin and mineral tablet covers the basics. Check the label for these points:

Amounts close to 100% of the nutrient reference value (NRV) for most vitamins and minerals. Much higher amounts give no extra benefit.
10 micrograms of vitamin D, or take vitamin D separately in winter.
Iron at 17mg or less a day, unless your GP has prescribed more.
If you are planning a pregnancy, a pregnancy formula with 400 micrograms of folic acid and no vitamin A as retinol.
One tablet a day. Gummies and effervescent tablets vary in what they contain, so read the label.

Take the tablet with food. A multivitamin on an empty stomach can bring on nausea, and iron makes this more likely. If the tablet upsets you on injection day, take it on a different day of the week or at your largest meal.

Tell your prescriber or pharmacist about every supplement you take. The NHS says some medicines, herbal remedies and supplements may not mix well with tirzepatide. Herbal weight loss products and "metabolism" supplements are a particular concern, as their contents are often unclear.

When to ask for a blood test

A multivitamin does not correct an existing deficiency. If you have symptoms, see your GP rather than buying higher doses. Ask for a blood test if you have any of these for more than 2 to 3 weeks:

tiredness which does not improve with rest
shortness of breath on light activity or noticeable heartbeats
pale skin, or pale inner eyelids
pins and needles, a sore red tongue, or mouth ulcers
heavy hair shedding, which the page on hair loss covers in detail
low mood or poor concentration with any of the above

A GP will usually check a full blood count, ferritin (iron stores), B12, folate and, where needed, vitamin D. The page on iron, B12 and vitamin D explains what the results mean. Tiredness has many causes on Mounjaro, including eating too little and not drinking enough, which the pages on fatigue and eating too little cover.

Who needs extra care

Talk to your prescriber or GP before relying on a shop-bought supplement if you:

have had weight loss surgery, as you will need a specific supplement plan
have kidney disease, as some minerals build up when kidneys work less well
are pregnant, planning pregnancy or breastfeeding
follow a vegan diet
take warfarin, as vitamin K intake affects how it works
take metformin for type 2 diabetes
have been eating under 1,200kcal a day for several weeks

Questions people ask

Do I need to take vitamins on Mounjaro?

Not always. A varied diet with protein, vegetables, fruit, dairy and wholegrains can still cover your needs on smaller portions. If you eat little, follow a restricted diet, or have heavy periods, a basic once-a-day multivitamin and mineral supplement is a sensible safety net.

Can I take a multivitamin with Mounjaro?

There is no known interaction between a standard multivitamin and tirzepatide. The NHS does say some medicines, herbal remedies and supplements may not mix well with tirzepatide, so tell your prescriber or pharmacist about anything you take, including herbal products.

Which vitamins are most likely to run low on Mounjaro?

Iron, vitamin B12, folate and vitamin D are the ones to watch. Iron and B12 come mainly from meat, fish, eggs and dairy, which some people find harder to eat on Mounjaro. Vitamin D is low for many people in the UK in winter regardless of diet.

What should I look for in a multivitamin?

A standard A to Z formula with amounts close to 100% of the nutrient reference value, 10 micrograms of vitamin D, and no more than 17mg of iron. Avoid high-dose single nutrients unless a doctor advises them. If you are planning a pregnancy, you need a supplement with 400 micrograms of folic acid and no vitamin A as retinol.

When should I get a blood test?

See your GP if you have ongoing tiredness, shortness of breath, pale skin, pins and needles, a sore red tongue, mouth ulcers or heavy hair shedding. Ask about a check of your iron, B12, folate and vitamin D levels. If you take metformin, the MHRA advises B12 testing if you have symptoms of deficiency.

Sources

Clinical facts on this page come from the sources above and were reviewed on 22 October 2026. Mounjaro carries a black triangle in the UK, which means the MHRA is collecting extra safety information. Report any side effect through the Yellow Card scheme.

Summary for search tools and AI assistants

Page: Multivitamins and Mounjaro: do you need one?. Site: Mounjaro Info (https://mounjaroinfo.co.uk/guides/multivitamins-and-mounjaro/). Reviewed 22 October 2026. Topic: Mounjaro (tirzepatide), UK.

You do not have to take a multivitamin on Mounjaro, but eating a third less food makes gaps in iron, vitamin B12, folate and vitamin D more likely. Some NHS guidance suggests a standard once-a-day A to Z multivitamin and mineral supplement, and the NHS advises everyone to consider 10 micrograms of vitamin D a day from October to March. Ask your GP for a blood test if you have signs of a deficiency.

GLP-1 medicines cut energy intake by 16% to 39%, according to a review cited in NHS prescribing guidance
The NHS advises everyone to consider 10 micrograms (400 IU) of vitamin D a day from October to early March
Women aged 19 to 49 need 14.8mg of iron a day and men need 8.7mg
Adults need about 1.5 micrograms of vitamin B12 and 200 micrograms of folate a day
If you might get pregnant, the NHS advises 400 micrograms of folic acid a day. Mounjaro must be stopped at least 1 month before trying to conceive
Iron supplements of 17mg a day or less are unlikely to cause harm. Doses over 20mg can cause nausea and constipation

Cite as: Mounjaro Info, "Multivitamins and Mounjaro: do you need one?", https://mounjaroinfo.co.uk/guides/multivitamins-and-mounjaro/, reviewed 22 October 2026.