Choosing the best multivitamin while on Mounjaro

Why micronutrient gaps open up faster than most people expect

The SURMOUNT-1 trial, published in the New England Journal of Medicine, documented average body-weight reductions of around 20–21% at the 15 mg tirzepatide dose over 72 weeks. That scale of weight loss reflects a significant sustained reduction in calorie intake, and with fewer calories come fewer vitamins and minerals, even in people eating a reasonably balanced diet. Protein tends to fall too, which compounds the issue because protein is needed to carry and use several B vitamins efficiently.

NHS guidance on weight-management medicines notes that people on GLP-1 and dual-agonist treatments should pay particular attention to dietary quality precisely because portion sizes shrink so dramatically. Slowed gastric emptying, one of tirzepatide's mechanisms, means food (and whatever micronutrients it contains) moves through the stomach more slowly. That is useful for satiety, but it also means the absorption window for some oral nutrients shifts. Taking your multivitamin at least 30 minutes before a meal rather than swallowing it alongside food is a practical habit that many people on tirzepatide find works better for them, a simple check you can build into a morning routine in under a minute.

A final structural point: if you are eating under roughly 1,200–1,400 kcal per day, a multivitamin alone may not fully compensate. Your prescriber can order a blood panel to check serum B12, ferritin, vitamin D and folate levels; that data is far more useful than guessing from symptoms.

The four nutrients to check on any label you pick up

Not all multivitamins are built the same, and the UK market is not regulated the same way medicines are. When you are reading a label, four nutrients deserve your attention first.

Vitamin D3 is the form most readily used by the body. The UK Chief Medical Officers already recommend 10 micrograms (400 IU) daily for the general population through autumn and winter; on a low-calorie regimen with reduced oily fish and egg intake, that baseline can easily slip. Look for D3 (cholecalciferol) rather than D2 on the label.

Vitamin B12 absorption depends partly on stomach acid and intrinsic factor. Slower gastric transit can subtly disrupt this. A formulation that provides at least 2.5 micrograms (around 100% of the UK RNI) is a reasonable floor; some people with borderline levels do better with a sublingual or methylcobalamin form, but discuss that with your prescriber rather than self-treating a deficiency.

Iron is worth checking especially for women of reproductive age, who are already more likely to have borderline stores. Look for ferrous forms (ferrous fumarate or ferrous bisglycinate) which are generally gentler on the gut than ferric sulphate, relevant when nausea is already a factor on treatment. Our guidance on the best multivitamin options for women on Mounjaro goes into this in more detail.

Folate (as methylfolate where possible) rounds out the set. It is easily depleted on a calorie-restricted diet and is particularly important for anyone who might become pregnant, given that Mounjaro is not recommended during pregnancy.

What to look for beyond the headline four

Zinc and magnesium often fall short on very-low-calorie diets and both play roles in immune function and muscle recovery, relevant when you are combining treatment with increased physical activity, as the full vitamins and supplements guide for people on Mounjaro covers. Calcium is worth checking if dairy intake drops; aim for a multivitamin that provides at least 200–400 mg alongside whatever you get from food, rather than a single high-dose calcium tablet which can interfere with iron absorption if taken together.

A note on fat-soluble vitamins: A, D, E and K are stored in body fat, and rapid fat loss can temporarily alter how these are metabolised. Megadoses of vitamin A (retinol form, above 1,500 micrograms daily) should be avoided; most standard multivitamins stay well below that, but it is worth a glance. Vitamin K2 has attracted interest as a supplement alongside D3 for bone health during weight loss, though the evidence base for that combination in a Mounjaro-specific context is still emerging.

For a detailed comparison of specific product formats, our page on the best multivitamin when taking Mounjaro is a useful starting point before you read labels in earnest. Cost context for treatment itself, if that is part of your planning, is covered on the Mounjaro cost page.

How to discuss supplements at your clinical consultation

Supplements are not a substitute for clinical oversight, and a multivitamin does not reduce the need for regular review. A GPhC-registered Independent Prescriber at a service like nume can review your full picture (current diet, any existing deficiencies, other medications) before and during treatment. Some supplements interact with medicines: high-dose iron can interfere with levothyroxine absorption, for example, and fat-soluble vitamins accumulate if over-supplemented.

The honest answer to the question of which specific product to buy is that the best choice varies by individual. A blood test before you start gives you a baseline; a repeat at around three to six months tells you whether the gap is closing. That evidence beats any list of branded recommendations. NHS guidance on tirzepatide on the NHS medicines pages and the NHS England wrap-around care guidance both emphasise dietary support as part of treatment, not an afterthought. If you are weighing up whether tirzepatide is right for you, the free consultation at nume is the place to start, a real prescriber reviews your answers the same day.