If you are looking for vitamins to take with Mounjaro, there is no single list that suits everyone.
For adults in the UK using Mounjaro for weight loss, if you have been eating substantially less or have symptoms that could indicate a deficiency, your GP can advise whether blood tests are appropriate before you start supplements,
Mounjaro can reduce appetite and delay gastric emptying, which may make it harder for some people to maintain an adequate nutritional intake.
Common nutrients that sometimes need attention include vitamin B12, iron, vitamin D and calcium, but whether you need them depends on your diet, symptoms and test results. This guide explains which nutrients are most worth monitoring, why testing beats guessing, how to think about multivitamins, what to do about hair loss during weight loss, when to speak to a GP instead of self-supplementing, and how to use supplements more safely if you do need them.
Mounjaro is a prescription-only medicine and should be used under the supervision of an appropriately qualified prescriber. Nothing here replaces personalised advice from your GP, pharmacist or dietitian.
Start With a Blood Test, Not a Supplement
Taking supplements without knowing your levels has three problems.
You may take something you do not need, which does nothing except cost money.
You may miss the thing you are actually low in.
And some nutrients cause harm in excess, so blind supplementation is not risk-free.
Ask your GP whether blood tests are appropriate, particularly if you have been eating substantially less for several months or have symptoms that could indicate a deficiency.
Depending on your symptoms and history, your GP may consider tests such as a full blood count, ferritin, vitamin B12, folate, vitamin D or thyroid function.
Nutrients Most Worth Attention
These are the ones that come up most often when intake has dropped substantially. Presence on this list is not a recommendation to supplement.
Vitamin B12
B12 is mainly found in animal foods, so eating less may reduce your intake. Low B12 can cause fatigue, weakness, pins and needles and difficulty concentrating, which can sometimes be mistaken for treatment side effects.
Taking folic acid can mask some signs of B12 deficiency while nerve damage continues, so it is better to check your B12 level before taking supplements.
If you also take metformin, B12 is worth checking because long-term use can lower B12 levels.
Iron
Low iron is common, particularly in menstruating women, and low dietary iron intake can contribute to deficiency, particularly when combined with other risk factors such as heavy periods. Iron is essential for producing healthy blood cells, and low levels can cause fatigue, breathlessness, pallor and feeling cold.
Iron is the clearest example of why testing matters. Excess iron accumulates and causes organ damage, and some people carry genetic variants that make them prone to this. Iron supplements should not be taken speculatively.
Vitamin D
Vitamin D is produced in the skin in response to sunlight and is also obtained from a small number of foods. Vitamin D deficiency affects about 1 in 6 adults in the UK. UK guidance suggests considering a daily supplement during the autumn and winter months for most people, and year-round for some groups, because vitamin D supports calcium absorption and bone health.
This is the one nutrient where general population guidance exists independently of your treatment. Follow NHS guidance and check the current recommendation, as vitamin D is recommended to help prevent deficiencies that affect bone health.
Protein
Protein is not a vitamin, but it is important during weight loss because it helps support muscle maintenance.
Some weight loss can include lean tissue as well as body fat. Adequate protein and resistance exercise can help support muscle maintenance. On a substantially reduced appetite, hitting protein needs is genuinely difficult, and muscle loss affects strength, metabolic rate and how you feel.
If you do one thing nutritionally on treatment, prioritise protein at every meal. A dietitian can help you work out what that looks like for you, and protein supplements such as protein powder can help if dietary intake is too low to preserve muscle mass.
Calcium
Often falls alongside reduced dairy intake, and matters for bone health during weight loss. Calcium is important for bone health, particularly when overall intake is low or bone health is already a concern.
Other Nutrients
Other nutrients, including folate, zinc and magnesium, may become relevant if food intake is very restricted or your diet lacks particular food groups. Whether supplementation is needed depends on your diet and individual circumstances.
| Nutrient | Why it matters here | Signs of low levels |
|---|---|---|
| B12 | Reduced animal foods; metformin interaction | Fatigue, pins and needles, fogginess |
| Iron | Reduced red meat; menstrual losses | Fatigue, breathlessness, feeling cold, pallor |
| Vitamin D | Widely low in the UK regardless of diet | Often none until significant |
| Protein | Muscle preservation during weight loss | Weakness, poor recovery, hair thinning |
| Calcium | Reduced dairy; bone health | Usually none until significant |
Is a Multivitamin Worth Taking?
A standard multivitamin may be useful for some people whose diet has become more limited, but it is not routinely needed by everyone taking Mounjaro, but it should complement whole foods and balanced meals, not replace them. It is not a substitute for testing, and it will not correct a genuine deficiency, which usually needs targeted treatment at higher levels than any multivitamin provides.
If you choose one, sensible principles:
- A standard formulation rather than a high-potency one, unless advised otherwise.
- Avoid "mega dose" products, particularly those with high vitamin A.
- Check you are not doubling up if you already take something specific.
- Take it with food, and check tolerance if you are prone to nausea.
- Choose a reputable brand; dietary supplements are best used as a safety net, not a replacement for a balanced diet.
If you are considering an iron-containing supplement, check whether you actually need iron rather than taking it routinely. Anyone pregnant or planning pregnancy needs specific advice, as some supplements are unsafe in pregnancy and folic acid requirements differ.
There is no product specifically formulated for people on Mounjaro that offers anything a standard multivitamin does not, whatever the marketing says.
Hair Loss on Mounjaro
This drives a lot of supplement searching, so it deserves a direct answer.
Hair shedding during significant weight loss is common and usually reflects telogen effluvium, a response to the physiological stress of rapid weight change. Hair follicles shift into a resting phase and shed a few months later, which is why shedding often starts two to four months after weight loss begins rather than immediately.
The uncomfortable part: Hair shedding during significant weight loss can be a form of telogen effluvium, which may be triggered by physiological stress and nutritional changes. Biotin in particular is heavily marketed for hair and rarely helps, since biotin deficiency is genuinely rare. It can also interfere with some blood tests, including thyroid tests, which is worth mentioning to your GP if you take it.
What actually helps:
- Adequate protein, since hair is largely protein
- Checking iron, ferritin, B12 and thyroid function, as all four affect hair and all four are treatable
- Not losing weight faster than necessary
- Patience, as telogen effluvium is usually self-limiting and regrows over months
If shedding is severe, patchy rather than diffuse, or accompanied by other symptoms, see your GP rather than self-treating.
When Symptoms Need a GP, Not a Supplement
See your GP rather than reaching for a supplement, and seek medical advice promptly if symptoms are severe, persistent, or worsening, if you have:
- Persistent fatigue beyond what you would expect
- Breathlessness on mild exertion
- Pins and needles, numbness or unsteadiness
- Unusual pallor
- Persistent dizziness
- Heart palpitations
- Severe or patchy hair loss
- Cognitive symptoms such as memory or concentration difficulty
- Mouth ulcers or a sore tongue
- Significant or persistent stomach pain
These symptoms can have several causes, including anaemia, vitamin B12 deficiency or thyroid problems, so persistent symptoms are worth discussing with your GP.
Practical Points
Timing
If a tablet causes nausea, taking it with food or at a different time of day often helps. Discuss timing with your pharmacist if you take other medicines.
Persistent diarrhoea or vomiting can make it harder to maintain adequate fluid and food intake. Speak to your prescriber if these symptoms are severe or ongoing.
Electrolyte supplements are not routinely needed, but your pharmacist or GP can advise if vomiting, diarrhoea or reduced fluid intake has caused dehydration or an electrolyte imbalance.
Interactions
Check with your pharmacist before starting supplements if you take other medication. Certain supplements and herbal supplements may affect blood sugar, blood glucose levels, and blood sugar control, so it is sensible to check with a healthcare provider before starting them.
Eating well still comes first
A balanced diet based on whole foods, adequate protein and a variety of nutrient-rich foods remains the foundation of good nutrition. Supplements should fill specific gaps rather than replace a varied diet.
Ongoing treatment.
Nutritional status and any supplement plan are reasonable things to review periodically on long-term treatment, especially as part of a weight loss journey or broader weight management plan with weight loss injections. More on Mounjaro treatment is on the product page.
