The best vitamins for women on Mounjaro: what the evidence actually says

What reduced food intake does to micronutrient levels

The SURMOUNT-1 trial, published in the New England Journal of Medicine, showed average body-weight reductions of around 20–21% at the 15 mg dose over 72 weeks. That level of calorie reduction is real and sustained. When overall food volume drops that sharply, the nutrients that were already marginal in many women's diets (iron, vitamin D, magnesium, folate) can drop further still.

Gastric emptying slows on tirzepatide, which affects how quickly food moves through the upper gut. This does not necessarily impair absorption of every nutrient, but it changes the digestive environment. Women who are also vegetarian, have heavy periods, follow a dairy-free diet, or are in perimenopause are starting from a more depleted baseline, so the gap between what food provides and what the body needs can widen faster.

There is no MHRA or NICE guidance mandating a specific supplement list for tirzepatide users. What does exist is a body of clinical practice guidance, and the NHS medicines page for tirzepatide recommends following a reduced-calorie diet alongside treatment, which in turn supports the case for reviewing your diet's nutritional completeness. The practical implication is that women on Mounjaro should not assume smaller meals are still delivering their full nutritional requirements.

Iron and folate: the two nutrients women most often run short on

Iron deficiency is already the most common nutritional deficiency in UK women of reproductive age, according to NHS data. Mounjaro does not directly block iron absorption, but eating less red meat, fewer fortified cereals and smaller portions overall reduces dietary iron intake. Fatigue on tirzepatide can have several causes; low iron is one of them and is worth ruling out with a blood test rather than guessing.

Folate (vitamin B9) matters for women who could become pregnant, the Department of Health recommends 400 micrograms daily before conception and through the first 12 weeks of pregnancy. Mounjaro is not recommended during pregnancy, and women who might conceive should discuss this with their prescriber. But folate is also relevant beyond reproduction: it supports red blood cell production and is often low in restrictive eating patterns. A good-quality B-complex or a dedicated folate supplement is the usual practical answer.

If you want a closer look at how supplement choices stack up against each other, our comparison of multivitamins for women on Mounjaro works through the label claims in more detail.

Vitamin D, calcium and bone health across the years on treatment

Vitamin D deficiency is widespread in the UK regardless of weight-loss treatment, the NHS recommends that everyone in England considers a 10-microgram daily supplement through autumn and winter. For women on Mounjaro, the case is stronger. Significant weight loss, especially over months to years, can affect bone mineral density. Calcium and vitamin D work together to limit that loss, which is why they tend to be discussed as a pair.

Dairy foods are one of the most efficient dietary sources of calcium, but women who eat less overall, who are lactose-intolerant, or who have shifted away from dairy as part of a lower-calorie approach may not be hitting the 700 mg daily reference intake. A combined vitamin D3 and calcium supplement is straightforward; some women prefer to take them separately so they can adjust each dose independently. Either approach is reasonable, the conversation with your prescriber is where the dosing gets personalised.

Bone health is also one reason that strength training is often recommended alongside GLP-1 treatment, as resistance exercise supports bone density in a way that cardio alone does not. Supplements assist; they do not replace load-bearing activity. You can read more about the broader picture on our guide to vitamins to take on Mounjaro.

B12, magnesium and the supplements that often get overlooked

Vitamin B12 deserves its own paragraph. It is found almost exclusively in animal products, and its absorption depends partly on a compound called intrinsic factor produced in the stomach. Reduced food intake, less red meat and fewer fortified foods can all chip away at B12 levels over months. The tricky thing is that deficiency develops slowly, nerve tingling, fatigue, low mood and poor concentration can take a year or more to appear, by which point stores are genuinely depleted. Women who eat little meat or fish are at particular risk.

Magnesium sits quietly in the background of hundreds of enzymatic processes: sleep quality, muscle recovery, mood regulation and energy metabolism among them. It is found in nuts, seeds, legumes and wholegrains, foods that tend to shrink in portion size as appetite falls. Many women report that a magnesium glycinate supplement (glycinate is generally better tolerated than oxide) improves sleep and reduces the muscle cramps that occasionally accompany rapid weight loss.

Omega-3 fatty acids are worth a mention too. They are not vitamins in the strict sense, but they support cardiovascular health and mood, and their dietary source (oily fish, walnuts, flaxseed) is easy to undereat on a reduced-calorie plan. If you are weighing up which supplements to prioritise alongside treatment, our guide to the best vitamins when on Mounjaro covers exactly that question in one place.

For a full rundown of what individual supplements actually do in this context, this page on which vitamins you need on Mounjaro goes through each nutrient systematically. And if you are considering the cost of treatment alongside any supplement budget, the Mounjaro cost page lays out how private pricing works in the UK.

One practical note: a lot of women find it easiest to take vitamins first thing in the morning, before breakfast, which is roughly when the tablet reminder goes off anyway if they're on the oral route, so it becomes part of the same small ritual. Habits that piggyback on an existing one tend to stick. That said, iron can interact with calcium if taken at the same time, so spacing them a few hours apart is worth doing if you take both.

If you would like to discuss your nutritional needs alongside your treatment plan, a prescriber at nume (sorry, our clinical team) reviews every consultation personally. Check your eligibility and we can take it from there.