Vitamin and mineral deficiencies can be a concern during Mounjaro treatment, particularly when reduced appetite means you are eating less or a narrower range of foods. A large 2025 observational study of 461,382 adults starting GLP 1 receptor agonist treatment found that 22.4% had at least one recorded nutritional deficiency or deficiency related complication within 12 months. Vitamin D deficiency was the most commonly recorded nutritional deficiency, affecting 13.6% of people at 12 months.
It is important to put these findings into context. The study looked at GLP 1 receptor agonists as a group rather than Mounjaro specifically, and it was based on recorded diagnoses rather than routine blood tests. This means the results do not show that Mounjaro directly causes vitamin deficiencies, and the risk can vary from person to person.
This guide explains which nutrients may need attention during Mounjaro treatment, why reduced food intake can matter, what signs to look out for, and when it may be appropriate to speak with your prescriber about nutritional support.
None of this means you need to avoid Mounjaro. The aim is simply to make sure your nutritional needs are not overlooked while your appetite and food intake change.
Key things to know
- More than 1 in 5 people in a large observational study of GLP 1 receptor agonist users had a recorded nutritional deficiency or deficiency related complication within 12 months. Vitamin D was the most commonly recorded deficiency.
- Reduced food intake may make it harder to get enough vitamins, minerals and protein, particularly if your appetite remains low for a prolonged period.
- The available evidence does not show that Mounjaro directly prevents your body from absorbing vitamins and minerals. More research is needed to understand the different factors involved.
- There is currently limited evidence and no dedicated UK monitoring framework specifically for nutritional deficiencies caused by GLP 1 medicines.
- Vitamin D, B vitamins, iron and other nutrients may need attention depending on your diet, existing health conditions and individual risk factors. However, not everyone taking Mounjaro will develop a deficiency.
How Mounjaro May Affect Your Nutritional Status
Mounjaro works on GIP and GLP 1 receptors involved in appetite regulation. It can reduce hunger and increase feelings of fullness, which can lead to eating less overall. For some people, this may make it harder to get enough protein, vitamins and minerals from food, particularly if their diet becomes more limited.
Reduced food intake is currently one of the main explanations for why nutritional deficiencies may occur during GLP 1 treatment. However, the available research is still developing, and other factors may also contribute. Some reviews have discussed delayed gastric emptying and possible changes in nutrient handling, but these effects are not yet fully understood.
This is different from some forms of weight loss surgery, where changes to the digestive system can directly affect nutrient absorption. With Mounjaro, the main concern is more likely to be whether you are eating enough of a varied diet to meet your nutritional needs.
How Common Is Vitamin Deficiency on Mounjaro?
A 2025 retrospective study of 461,382 adults starting GLP 1 receptor agonist treatment found that 12.7% had a recorded nutritional deficiency within 6 months, rising to 22.4% within 12 months. Vitamin D deficiency was the most commonly recorded individual deficiency, affecting 7.5% at 6 months and 13.6% at 12 months. Other recorded problems included B vitamin deficiencies, nutritional anaemia, iron deficiency anaemia and mineral deficiencies.
However, these figures should not be interpreted as the percentage of Mounjaro users who will definitely develop a deficiency. The study covered GLP 1 receptor agonists as a class and used healthcare records to identify diagnosed deficiencies. It also included people with different health conditions, and most participants had type 2 diabetes.
Nutritional deficiencies can also be present before treatment begins. Obesity and some underlying health conditions are already associated with a higher risk of certain vitamin and mineral deficiencies. This means your nutritional status may depend on several factors, including your diet, existing health, other medicines and how much your food intake changes during treatment.
Key Vitamins and Minerals at Risk
| Nutrient | Why it's at risk |
|---|---|
| Vitamin D | The single most common deficiency reported, compounded by already-widespread low levels in the UK population |
| B12, thiamine and other B vitamins | Not stored extensively in the body, so intake needs to stay consistent; reduced consumption of B-vitamin-rich foods is common as appetite falls |
| Iron | Reduced intake of red meat and other iron-rich foods, particularly relevant for women |
| Calcium, magnesium and potassium | Frequently fall below recommended intakes as overall food volume decreases |
| Protein | Often falls below the 1.2-2.0g per kg body weight needed to help protect muscle mass during rapid weight loss |
Fat-soluble vitamins A, D, E and K also deserve attention, since they require dietary fat for absorption, and calorie-restricted eating patterns can reduce fat intake alongside overall food volume.
Recognising the Signs of Vitamin Deficiency
Fatigue and weakness can occur with several vitamin and mineral deficiencies, including iron, vitamin B12 and vitamin D deficiency. However, these symptoms can also have many other causes, including weight loss, changes in diet or other health conditions. It is therefore better to speak with a healthcare professional rather than trying to diagnose a deficiency based on symptoms alone.
Neurological symptoms also deserve attention. Tingling or numbness in the hands and feet, memory problems, or changes in mood can occur with vitamin B12 deficiency. If a B12 deficiency is left untreated for a long time, it can cause nerve damage, which may not always be completely reversible. If you notice these symptoms, speak with your prescriber or another healthcare professional rather than waiting for them to go away.
Changes to your hair, skin or nails can have several possible causes. Nutritional deficiencies, including deficiencies in iron or zinc, may sometimes contribute to these changes. Hair thinning can also occur during significant weight loss, so noticeable or ongoing hair loss is worth discussing with a healthcare professional rather than assuming it is simply part of treatment.
Is There Official UK Guidance on Nutrient Monitoring for GLP 1 Medicines?
There is not currently a dedicated UK nutrient monitoring guideline specifically for people taking GLP 1 medicines such as Mounjaro. This is different from bariatric surgery, where the British Obesity and Metabolic Surgery Society (BOMSS) provides guidance on nutritional monitoring and supplementation.
A 2025 review published in Nutrients highlighted the limited evidence and lack of formal nutritional monitoring protocols specifically for GLP 1 medicines. It suggested that lessons from existing bariatric surgery guidance could help inform future approaches, although more research is needed before a standard monitoring schedule can be recommended for everyone taking these medicines.
What Sensible Monitoring Looks Like in Practice
Because there is no fixed UK monitoring schedule for nutritional deficiencies during GLP 1 treatment, the approach can vary from person to person. Depending on your medical history, diet, symptoms and other risk factors, your prescriber may decide that blood tests are appropriate.
These may include tests such as a full blood count, vitamin B12, folate, vitamin D and iron studies. The exact tests and timing should be based on your individual circumstances rather than following one routine schedule for everyone.
Some people may need closer attention to their nutritional status. This can include people with a restricted diet, previous bariatric surgery, conditions that affect nutrient absorption, or medicines that can affect certain nutrient levels. For example, long term use of metformin or proton pump inhibitors can be associated with lower vitamin B12 levels in some people.
If you are concerned about your diet or notice symptoms that could suggest a deficiency, speak with your prescriber. They can decide whether testing or dietary advice is appropriate for you.
Dietary Strategies to Reduce Your Risk
When your appetite is lower, choosing foods that provide plenty of nutrients in smaller portions can help you make the most of what you eat. Including a source of protein at each meal can also help you maintain adequate protein intake while your overall food intake is reduced. Your individual protein needs depend on factors such as your body size, activity levels, age and overall health.
Good protein sources include lean meat, fish, eggs, dairy products, beans and lentils. Vitamin B12 is naturally found mainly in foods such as meat, fish, eggs and dairy products, while fortified foods can also provide B12.
Try to include a variety of nutrient rich foods, such as vegetables, fruit, whole grains, beans, nuts, seeds, dairy or suitable alternatives, and healthy sources of fat. Smaller meals may also feel easier to manage if Mounjaro has reduced your appetite.
Iron can be found in foods such as lean red meat, beans, lentils, nuts and fortified cereals. Oily fish can provide vitamin D, while vitamin D also comes from sunlight and some fortified foods. Your requirements will vary, so do not assume that you need a supplement simply because you are taking Mounjaro.
Staying hydrated is also important, particularly if nausea, vomiting or diarrhoea makes it harder to eat and drink normally. Some people consider probiotics when experiencing gastrointestinal symptoms, but evidence for their specific benefits in people taking GLP 1 medicines remains limited. If you are considering a vitamin, mineral or other supplement, it is sensible to discuss it with your pharmacist or prescriber first.
Supplementation Considerations
Mounjaro supplements are not automatically needed. Whether you need one depends on factors such as your diet, symptoms, existing health conditions and, where appropriate, blood test results. Supplements can help fill specific nutritional gaps when diet alone is not enough, but they should not replace a varied, balanced diet.
If you are struggling to maintain a varied diet because of reduced appetite, your prescriber or pharmacist may discuss whether a standard multivitamin is appropriate. Many multivitamins contain a range of vitamins and minerals, but the amounts vary considerably between products. A higher strength product is not necessarily better, and taking unnecessary amounts of certain vitamins and minerals can cause problems.
If testing shows a specific deficiency, a targeted supplement may be more appropriate than a general multivitamin. For example, iron or vitamin B12 may be recommended when there is a confirmed deficiency or a clear clinical reason to supplement. Iron supplements can cause side effects such as nausea and constipation, so they are best taken when advised by a healthcare professional.
UK dietary reference values recommend 1.5 micrograms of vitamin B12 per day for adults. Iron requirements vary by age and sex. For example, the reference nutrient intake is 8.7mg per day for adult men and women aged 50 and over, and 14.8mg per day for women aged 19 to 50. These are dietary reference values rather than a recommendation for everyone to take an iron supplement.
Calcium supplements may sometimes be appropriate when dietary intake is inadequate or when a healthcare professional recommends them. They can cause side effects such as constipation in some people.
The way you take a supplement can also matter. Fat soluble vitamins, including vitamins A, D, E and K, are generally absorbed better when taken with a meal containing some fat. Other supplements have different instructions, so check the product information or ask your pharmacist about the best timing.
Be particularly careful with high dose supplements and herbal products. Some can interact with medicines or cause side effects, while taking too much of certain nutrients can be harmful. If you are taking several medicines, including diabetes treatments, it is worth checking any new supplement with your pharmacist or prescriber first.
Higher Risk Groups Needing Extra Attention
Some people may have a higher risk of nutritional deficiencies while taking Mounjaro. This can include older adults, people with a restricted diet, people with conditions that affect nutrient absorption, and those who already have a nutritional deficiency before treatment begins.
Women who could become pregnant may also need particular attention to nutrients such as folate and iron. Mounjaro should not be used during pregnancy, and if you are planning a pregnancy, speak with your prescriber about your treatment.
If you take metformin, it is worth mentioning this to your prescriber. Long term metformin treatment can be associated with lower vitamin B12 levels in some people. Long term use of proton pump inhibitors can also affect the absorption of vitamin B12 and iron in some circumstances.
Vegetarians and vegans may need to pay particular attention to nutrients such as vitamin B12, iron and zinc, especially if their overall food intake falls during treatment. This does not mean that deficiencies are inevitable, but making sure your diet remains varied and discussing supplementation or testing with a healthcare professional may be helpful.
Getting Started with Mounjaro at EverydayMeds
Mounjaro is available through EverydayMeds for weight management following a clinical consultation with a UK licensed prescriber. During the consultation, your prescriber can review your medical history, current medicines, suitability for treatment and any nutritional factors that may need attention.
This assessment can help make sure Mounjaro fits into your wider treatment and weight management plan rather than being considered in isolation.
Pricing starts from £169.99 for a single 2.5mg pen at the standard rate. New customer and returning customer discounts may also be available. As promotional pricing can change, check the current price at checkout or during your consultation.
Medical Disclaimer
This page provides general information about nutritional considerations during Mounjaro treatment and is not a substitute for personalised medical advice.
Mounjaro can cause gastrointestinal side effects such as vomiting and diarrhoea. These can lead to fluid loss and, in more significant cases, dehydration or changes in electrolyte levels. If you have significant fluid loss, your healthcare professional can advise whether an oral rehydration solution or electrolyte replacement is appropriate.
Similar gastrointestinal side effects can occur with other medicines used for weight management.
Blood tests and supplements should be considered based on your individual circumstances and discussed with your prescriber. Some supplements can affect blood glucose levels or interact with medicines used to manage diabetes, so check with a healthcare professional before starting a new supplement.
Tell your prescriber if you develop symptoms such as ongoing tingling, numbness or memory changes, as these can have several possible causes and may need assessment. Persistent vomiting, severe stomach pain, or signs of a serious allergic reaction require prompt medical attention. If you have severe or persistent symptoms, particularly alongside signs of dehydration such as marked weakness, dizziness or very little urine, seek urgent medical advice.
