Vitamins and Supplements on Mounjaro or Ozempic: What You Actually Need

The main way Mounjaro, Zepbound, Ozempic and Wegovy affect your vitamins and minerals is simple: they cut how much you eat by 16 to 39%, and less food means less of everything in it. The nutrients most likely to run short are vitamin D, calcium, iron and vitamin B12, with thiamin (vitamin B1) a particular risk if you're vomiting. Most people can cover them with protein-rich, nutrient-dense food plus vitamin D in autumn and winter, and let a blood test guide anything beyond that.

What studies of GLP-1 users have found

A 2026 review pulled together six studies covering about 481,000 adults on GLP-1 medications:

• Vitamin D deficiency was the most common problem, affecting 7.5% of users at 6 months and 13.6% at 12 months.
• Iron stores were lower: ferritin, the blood marker for stored iron, was 26 to 30% lower than in people on a comparison medicine.
• More than 60% ate less calcium and iron than they needed, and vitamin D intake averaged about a fifth of the recommended amount.
• Thiamin and B12 shortfalls grew over time.

These were observational studies, so they show a pattern rather than proof that the medication caused it. And many people start behind: in a US national survey, adults who qualify for GLP-1 treatment were already slightly more often short of magnesium, potassium and vitamins A, C, D, E and K.

The 2025 joint advisory from four US obesity and nutrition societies warns that vitamins and minerals get hard to cover below about 1,200 kcal a day for women and 1,800 for men, and that vomiting and diarrhea can make shortfalls worse. How much to eat on a GLP-1 covers those floors.

The nutrients to watch

Vitamin D. Few foods contain much of it: oily fish, egg yolks, red meat and fortified foods. In the UK, the sun isn't strong enough to make it between October and early March, so the NHS advises everyone to consider a daily 10 microgram supplement in autumn and winter, and all year if you're rarely outdoors or have dark skin.

Calcium. Bones matter more when you lose weight fast. The advisory notes that losing a lot of weight quickly (14% or more over 3 to 4 months) is linked with significant bone loss, more so in women and older people. Strength training helps: in one trial, a year on a GLP-1 plus exercise preserved bone density, while the medication alone lowered it. Dairy is the easiest source; see exercise on a GLP-1.

Iron. Red meat often loses its appeal on these medications (see no appetite or food aversions). Women who have periods need almost twice as much iron as men. The NHS notes that tea and coffee can reduce how much iron you absorb, and iron tablets commonly cause constipation, nausea and stomach pain, side effects many people already have on a GLP-1. If you suspect you're low, get a blood test rather than guessing.

Vitamin B12 and folate. B12 is found naturally only in animal foods: meat, fish, milk, cheese and eggs. If you eat little of these, or none, you'll need fortified foods or a supplement; see plant-based eating on a GLP-1. Folate comes from leafy greens, broccoli, peas, chickpeas and beans, and the body keeps no long-term store of it. The NHS warns that B12 deficiency left untreated can cause lasting damage, including to the nerves.

Magnesium and zinc. Magnesium comes from nuts, spinach and wholemeal bread; zinc, which helps wounds heal, from meat, shellfish, cheese and bread. The NHS suggests 300 mg of magnesium a day for men and 270 mg for women, and 9.5 mg of zinc for men and 7 mg for women. Potassium is covered in electrolytes on a GLP-1.

Nutrient	UK adults	US adults	Good sources
Vitamin D	10 mcg	15 mcg (20 mcg over 70)	Oily fish, egg yolks, fortified foods
Calcium	700 mg	1,000 mg (1,200 mg for women over 50 and everyone over 70)	Milk, yogurt, cheese, fortified soya, sardines
Iron	14.8 mg for women 19 to 49; 8.7 mg for others	18 mg for women 19 to 50; 8 mg for others	Lean red meat, beans, lentils, fortified cereals
Vitamin B12	1.5 mcg	2.4 mcg	Meat, fish, milk, cheese, eggs
Folate	200 mcg	400 mcg	Leafy greens, peas, chickpeas, beans

The UK amounts are the NHS's; the US amounts are the National Academies' recommended intakes, as listed by MedlinePlus.

Thiamin (B1): the one to know about if you're vomiting

The body can't store thiamin, so you need some every day, according to the NHS. Good sources are wholegrain bread, peas, nuts and fortified cereals. If you're vomiting repeatedly or barely eating for days, it can run low.

A 2026 study of drug safety reports and published cases found 15 cases of Wernicke encephalopathy, a serious brain condition caused by thiamin deficiency, linked to GLP-1 medications, mostly semaglutide and tirzepatide. Almost all involved vomiting, weight loss or loss of appetite, and 7 of the 11 people followed up had lasting neurological problems. It's rare, but get urgent medical help for confusion, poor coordination or unsteadiness, or vision changes such as double vision, especially after days of vomiting. See managing nausea to stop it getting that far.

Food first, on a small appetite

The same protein foods that protect your muscle carry most of these nutrients: dairy brings calcium and B12, eggs and oily fish bring vitamin D and B12, lean meat brings iron, zinc and B12, beans and lentils bring iron, and chickpeas, beans and leafy greens bring folate. The advisory recommends building meals around nutrient-dense, minimally processed food: vegetables, fruit, whole grains, legumes, lean protein, nuts and seeds. Protein targets on a GLP-1 shows how much protein to aim for.

Some recipes from the site built around those foods:

• Lemon-Herb Baked Salmon with Greens: oily fish for vitamin D and B12, 29 g protein
• High-Protein Greek Yogurt Bowl: dairy for calcium and B12, 26 g protein
• Ozempic Eggs: eggs and cheese for vitamin D, B12 and calcium, 30 g protein
• Lean Beef and Broccoli Stir-Fry: lean red meat for iron, zinc and B12, 38 g protein
• High-Protein Red Lentil Soup: lentils for iron, 24 g protein
• Tofu and Edamame Stir-Fry: edamame for iron, 27 g protein

Do you need supplements?

The advisory suggests considering supplements for the nutrients most at risk, such as vitamin D, calcium and B12, tailored to you, rather than a long list for everyone. In practice:

• Vitamin D. In the UK, the NHS autumn and winter advice applies to you like everyone else. Don't take more than 100 micrograms (4,000 IU) a day in total, the upper limit on both sides of the Atlantic.
• A multivitamin. The nutrients that run short on a GLP-1 are ordinary ones, so you don't need a product branded for GLP-1s. A standard multivitamin and mineral can be a sensible safety net if you're eating very little; just add up the vitamin D across everything you take.
• Iron. Take it if a blood test shows you need it, not on spec, for the side effects above.
• Magnesium. The advisory lists magnesium as an option for constipation, but more than 400 mg a day from supplements can cause diarrhea, according to the NHS. See constipation on a GLP-1.

Tell your prescriber or pharmacist what you take, so they can check it against your other medicines.

When to get checked

The advisory lists the signs of a nutrient shortfall: tiredness beyond what you'd expect, heavy hair loss, flaky or itchy skin, muscle weakness, wounds that heal slowly and unusual bruising. The NHS adds shortness of breath, noticeable heartbeats and pale skin for low iron, and pins and needles, a sore red tongue and memory problems for low B12 or folate. See also hair loss and fatigue.

A 2026 clinical review suggests checking vitamin D, B12, folate, iron (including ferritin) and zinc, plus thiamin in people at high risk. The advisory recommends rechecking nutrient levels during treatment, not just at the start. You're at higher risk if you:

• eat well under 1,200 kcal (women) or 1,800 kcal (men) a day
• have frequent vomiting or diarrhea
• eat a vegan or vegetarian diet
• have heavy periods
• are older, or a woman losing weight quickly, for bone health

General nutrition information, not medical advice. Talk to your prescriber or pharmacist before starting supplements, especially if you take other medicines.