Vitamins and Supplements on GLP-1 Treatment

Most people on Mounjaro (tirzepatide), Wegovy (semaglutide) or other GLP-1 medicines do not need a long list of supplements, and the product information does not require any. The real issue is that these medicines can cut food intake so much that it becomes harder to get enough vitamins and minerals from food alone. A 2025 joint advisory on nutrition and GLP-1 therapy suggested proactively considering supplements for nutrients at risk. For many people, that means following standard NHS vitamin D advice and possibly a basic multivitamin, while focusing on nutrient-dense food. This guide explains what is worth considering and what to avoid.

Why nutrient intake can fall on GLP-1 treatment

GLP-1 medicines reduce appetite and slow stomach emptying. Many people find they are eating a fraction of what they did before. That is how the treatment supports weight loss, but it also means fewer opportunities to take in vitamins, minerals, fibre and protein.

The 2025 joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society noted that insufficient intake of essential vitamins and minerals becomes more likely with calorie reduction, particularly at intakes below roughly 1,200 kcal a day for women and 1,800 kcal a day for men. It also pointed out that:

• the foods people still find appealing on treatment may be lighter, starchier or sweeter, and less nutrient-dense
• gastrointestinal side effects such as vomiting and diarrhoea can increase losses
• people who have had bariatric surgery, follow restrictive diets, or have certain medical conditions may already be at higher risk of deficiencies

Nutrients worth paying attention to

The advisory listed iron, calcium, magnesium, zinc and vitamins A, D, E, K, B1 (thiamine), B12 and C as nutrients that may be at risk. Here is what that means in practical terms.

Vitamin D

Vitamin D helps the body absorb calcium and supports bones, teeth and muscles. In the UK, most people cannot make enough from sunlight between October and early March. The NHS advises:

• everyone should consider a daily supplement of 10 micrograms of vitamin D during autumn and winter
• some groups should consider it all year round, including people who are rarely outdoors, those in care homes, people who usually wear clothes that cover most of their skin outdoors, and people with dark skin (for example, of African, African-Caribbean or south Asian background)
• adults should not take more than 100 micrograms (4,000 IU) a day unless a doctor advises it

This advice applies whether or not you are on GLP-1 treatment. Some people with obesity have lower vitamin D levels, which is another reason it is worth following.

Calcium

Calcium is important for bones, and rapid weight loss can affect bone density. Dairy foods, calcium-fortified plant drinks and yoghurts, tinned fish with soft bones (such as sardines), tofu set with calcium, and green leafy vegetables are good sources. If you eat little dairy or fortified alternatives, a dietitian may suggest a supplement. The NHS says that taking 1,500 mg or less of calcium supplements a day is unlikely to cause harm.

Iron

Iron is needed to make red blood cells. Low iron can cause tiredness, breathlessness and, in some people, hair shedding. According to the NHS, adult men need about 8.7 mg a day and women aged 19 to 49 need about 14.8 mg a day. People at higher risk of low iron include those with heavy periods, vegetarians and vegans, and people who eat very little red meat or fortified foods.

Iron supplements should generally be taken only if needed. The NHS notes that taking 17 mg or less a day from supplements is unlikely to cause harm, but higher doses can cause constipation, nausea, vomiting and stomach pain, which are already common on GLP-1 treatment. If you think you may be low in iron, ask your GP about a blood test rather than starting high-dose iron yourself.

Vitamin B12

B12 is found mainly in animal foods: meat, fish, eggs and dairy. Vegans need a reliable source, such as fortified foods or a supplement. People with type 2 diabetes who take metformin, and people on long-term acid-reducing medicines, are also at higher risk of low B12. Symptoms of deficiency can include tiredness, pins and needles, a sore tongue and memory problems. Your GP can check levels with a blood test.

Thiamine (vitamin B1)

Thiamine is found in wholegrains, pork, pulses, nuts and fortified cereals. Deficiency is uncommon in the UK, but it is a recognised concern when people have prolonged vomiting or very low food intake. This is one reason that persistent vomiting on GLP-1 treatment should always be reported to a clinician.

Magnesium and zinc

Magnesium is found in wholegrains, nuts, seeds, green leafy vegetables and pulses. Zinc is found in meat, shellfish, dairy, pulses and wholegrains. Both are covered by most standard multivitamin and mineral products. The NHS advises that taking 25 mg or less of zinc supplements a day is unlikely to cause harm.

Vitamins A, C, E and K

These are found across a varied diet: vitamin A in dairy, eggs, oily fish and orange or dark green vegetables; vitamin C in fruit and vegetables; vitamin E in plant oils, nuts and seeds; and vitamin K in green leafy vegetables. People eating a range of fruit and vegetables usually get enough. Note that high intakes of vitamin A over many years may affect bone health, so avoid taking more than one product containing it, and the NHS advises that people who are pregnant should not take vitamin A supplements.

Summary table: nutrients, food sources and when to consider a supplement

Should you take a multivitamin?

There is no trial evidence showing that people on GLP-1 medicines who take a multivitamin have better outcomes than those who do not. However, many clinicians regard a standard A to Z multivitamin and mineral, providing around 100% of reference intakes, as a sensible, low-risk safety net when food intake is greatly reduced.

If you choose one:

• pick a standard product at normal doses rather than "mega-dose" formulas
• check whether it already contains vitamin D, so you do not double up
• avoid taking several different supplements that contain the same nutrients
• choose a product without vitamin A if you are planning a pregnancy, and speak to your prescriber, because GLP-1 medicines for weight loss are not used in pregnancy
• take it with food if it upsets your stomach, or at a time of day when nausea is less of a problem

A multivitamin cannot replace the protein, fibre and many other beneficial compounds found in whole foods. Our guide to what to eat on GLP-1 medication and our sample meal plan show how to make small meals as nourishing as possible. Protein deserves special attention: see our guide to protein intake on weight loss injections.

Protein supplements

Protein shakes and powders are not vitamins, but they are the supplement people on GLP-1 treatment most often ask about. They can be useful for some people who struggle to meet protein needs from food, particularly on low-appetite days. Check labels for added sugar, and for sweeteners or sugar alcohols that may worsen wind or diarrhoea. People with kidney disease should not increase protein without medical advice.

Fibre supplements and laxatives

Constipation is very common on GLP-1 treatment. Food-first approaches (fruit, vegetables, wholegrains, pulses, prunes, kiwi fruit) plus fluids and activity are the usual starting point. If that is not enough, a pharmacist can advise on options such as:

• bulk-forming laxatives such as ispaghula husk, which must be taken with plenty of water
• osmotic laxatives such as macrogol, which draw water into the bowel

Leave a gap of at least an hour or two between fibre supplements and other oral medicines, as bulk-forming products can affect absorption. Our guide to constipation on GLP-1 medication covers this in detail.

Supplements to be cautious about

"Natural GLP-1" and weight-loss supplements

Some products are marketed as natural alternatives to GLP-1 medicines, or as supplements that "boost" GLP-1 or enhance the effect of your injection. These are sold as food supplements, not medicines. That means:

• they have not been through the licensing process that the MHRA uses to assess a medicine's safety, quality and effectiveness
• claims about weight loss or appetite are often based on limited or low-quality evidence
• some herbal ingredients can affect blood sugar or interact with other medicines
• quality and content can vary between products

If you are considering one, speak to a pharmacist first, particularly if you take medicines for diabetes, blood pressure, mental health or blood clotting.

Products bought online claiming to contain GLP-1 medicines

Any product sold without a prescription that claims to contain semaglutide, tirzepatide or another GLP-1 medicine is not a supplement. It is an unlicensed medicine, may be fake, and could be dangerous. Our guide to fake weight loss jabs explains the risks.

High-dose biotin

Biotin is often marketed for hair, skin and nails, and people sometimes take it for hair shedding on GLP-1 treatment. High doses can interfere with certain laboratory tests, including some thyroid and heart tests, leading to misleading results. If you take biotin, tell the person taking your blood. For more on hair, see our guide to Mounjaro and hair loss.

Very high doses of any single nutrient

More is not better. High doses of vitamin A, vitamin D, iron, zinc and vitamin B6, among others, can cause harm. Stick to standard doses unless a doctor recommends otherwise for a diagnosed deficiency.

Groups who may need extra attention

Vegetarians and vegans

Plant-based diets can be healthy and balanced, but when total food intake falls on GLP-1 treatment, some nutrients need particular attention. For vegans, these include vitamin B12 (which is not reliably found in unfortified plant foods), iodine, calcium, vitamin D, iron, zinc, selenium and omega-3 fats. Fortified plant drinks and yoghurts, fortified cereals and a suitable vegan supplement can help. A registered dietitian can review your diet.

People who have had bariatric surgery

People who have had weight-loss surgery usually already need lifelong vitamin and mineral supplements and regular blood tests. If you are starting a GLP-1 medicine after surgery, continue the supplements your bariatric team recommended and make sure your prescriber knows about your surgery. Our guide to GLP-1 medicines vs bariatric surgery covers the differences between the two approaches.

Older adults

Older people often have lower appetites, may absorb some nutrients, such as vitamin B12, less efficiently, and are more likely to be taking several medicines. They may also spend less time outdoors, which affects vitamin D. Our guide to GLP-1 medicines over 65 covers this.

People planning a pregnancy

GLP-1 medicines for weight loss are not used in pregnancy, and the product information advises stopping them some time before a planned pregnancy. The NHS recommends folic acid before conception and during early pregnancy. If you are planning a pregnancy, talk to your prescriber about when to stop treatment and about folic acid and other supplements. See our guide to GLP-1 medicines, pregnancy and fertility.

Supplements and your GLP-1 medicine

Injectable GLP-1 medicines

Common vitamins and minerals are not known to interact directly with injectable Mounjaro or Wegovy. However, GLP-1 medicines slow stomach emptying, which can affect how quickly some oral medicines are absorbed. This is mainly relevant for medicines where precise timing or blood levels matter. Our guide to GLP-1 medication interactions covers this in more depth.

Oral GLP-1 medicines

Oral semaglutide must be taken on an empty stomach with only a small amount of water, and you then need to wait before eating, drinking or taking other oral medicines and supplements. Taking a supplement at the same time could reduce how much of the medicine is absorbed. Always follow the patient information leaflet and your prescriber's instructions. Our oral GLP-1 hub explains tablet treatments.

If you have diabetes

Some supplements, particularly herbal products, may affect blood sugar. If you take insulin or a sulphonylurea alongside a GLP-1 medicine, you are already at increased risk of low blood sugar according to the product information. Check with your diabetes team before adding anything new.

Do you need blood tests?

Routine blood tests for vitamins and minerals are not required for everyone on GLP-1 treatment. But your GP may consider tests if you:

• have symptoms that could suggest a deficiency, such as persistent tiredness, breathlessness, pins and needles, a sore tongue or significant hair loss
• have had bariatric surgery
• follow a vegan or very restricted diet
• have prolonged vomiting or diarrhoea
• take medicines that affect nutrient absorption, such as metformin or long-term acid-reducing medicines

NICE guidance on obesity management recognises the importance of monitoring and support alongside weight-loss medicines. The level of monitoring offered varies between NHS services and private providers. If ongoing monitoring matters to you, it is worth asking about it. You can compare services on our providers page, and our weight loss injections hub covers the medicines themselves.

When to speak to a professional

Speak to your GP, prescriber or pharmacist if:

• you are unsure whether you need a supplement, or which one
• you take other medicines, especially warfarin, diabetes medicines, thyroid medicines or medicines for epilepsy
• you have kidney or liver disease, where some supplements may not be suitable
• you have symptoms of a possible deficiency, such as ongoing tiredness, breathlessness, pins and needles, a sore tongue or noticeable hair loss
• you are planning a pregnancy, because GLP-1 medicines for weight loss should be stopped in advance and your prescriber can advise on timing and folic acid
• you have a history of an eating disorder

Seek urgent help (call NHS 111, or 999 in an emergency) if you have:

• persistent vomiting that stops you keeping food or fluids down
• confusion, unsteadiness or problems with vision after a period of vomiting or very low intake
• severe abdominal pain that does not go away, with or without vomiting

Your prescriber is responsible for decisions about your GLP-1 treatment. A pharmacist is a good, accessible source of advice on supplements and possible interactions.