Which vitamins to take while on Wegovy (and what the evidence actually says)

The myth that 'less food means you need more of everything'

One of the most common misconceptions about GLP-1 medicines is that dramatically reducing your food intake automatically means you'll become deficient across the board and should take a broad-spectrum multivitamin to compensate. A well-chosen multivitamin isn't harmful, but it won't necessarily address the specific gaps most likely to emerge on semaglutide, and it may give a false sense of security if the nutrients that genuinely matter aren't among the higher-dose ingredients.

The more accurate picture: Wegovy works by reducing appetite and slowing gastric emptying. You eat less, you digest more slowly, and if your smaller meals aren't nutritionally dense, certain nutrients can drift lower over months. That's a manageable, targeted problem, not a reason to take ten different capsules each morning.

The NHS medicines page for semaglutide outlines the medicine's mechanism and common effects on digestion, which helps explain why food quality matters more than volume when you're on treatment. The goal is to get the nutrients you actually need from a smaller amount of food, supplementing where that's genuinely difficult.

A question our prescribers hear most weeks: "Should I just take a complete multivitamin and not worry about it?" The honest answer is that it depends entirely on what you're eating and what your blood results show, and there's no universal answer.

Vitamin D and B12: the two nutrients most worth supplementing

Vitamin D deserves mention first because the UK population as a whole has widespread insufficiency, entirely independent of weight-loss treatment. Public Health England has long recommended that adults consider 10 micrograms (400 IU) daily through autumn and winter at minimum. If you're eating less (and if fatty fish, eggs and fortified foods have fallen off the menu because appetite is low) your vitamin D intake from food may drop further. A blood test is the only way to know your actual level; some people on calorie-restricted diets are found to need a higher therapeutic dose under medical supervision.

Vitamin B12 is the other nutrient worth watching closely. B12 is found almost exclusively in animal products (meat, fish, dairy, eggs), and if nausea (one of the most common side effects in the early weeks) is making protein-rich foods unappealing, your dietary B12 can fall. B12 deficiency develops slowly but causes real problems: fatigue, nerve symptoms, and mood changes. A standard B-complex or a dedicated B12 supplement is inexpensive and low-risk for most adults. If you follow a plant-based diet, supplementation is essential regardless of Wegovy.

For a broader look at the nutritional context of weight-loss treatment, our guide to Wegovy and vitamins covers how semaglutide affects eating patterns and what that means in practice.

Iron, folate, protein: the supporting cast that people overlook

Iron and folate are worth mentioning, particularly for women of reproductive age. Iron deficiency is already common before weight-loss treatment begins; eating smaller portions of red meat or leafy greens can reduce dietary iron further. Symptoms (tiredness, breathlessness, difficulty concentrating) overlap with the general fatigue some people feel early in treatment, which makes deficiency easy to miss without a blood test.

Folate (vitamin B9) matters for cell repair and, critically, for anyone who may become pregnant. Wegovy is not recommended during pregnancy or while trying to conceive; contraception guidance is part of any clinical assessment before prescribing. But folate insufficiency has independent consequences and is worth maintaining through food (dark leafy greens, legumes, fortified cereals) or a basic supplement.

Protein isn't a vitamin, but it belongs in this conversation. On a significantly reduced calorie intake there's a real risk of losing muscle alongside fat if protein stays too low. Most adults on Wegovy benefit from making protein the non-negotiable part of every meal (aiming for a portion at breakfast, lunch and dinner) even when appetite is minimal. A dietitian can give you a personal target; our page on what vitamins to take on Wegovy touches on protein alongside the micronutrient picture.

How to approach supplementation practically

The most useful starting point is a conversation with your GP or prescriber before or shortly after starting Wegovy. A standard blood panel (vitamin D, B12, folate, ferritin, full blood count) gives you actual numbers rather than guesswork, and means you're targeting a real gap rather than hoping a general multivitamin covers it.

If a blood test isn't immediately available, a modest baseline is reasonable for most adults: vitamin D (10–25 micrograms daily), a B12 or B-complex supplement, and attention to iron-rich foods, and our guide to vitamins to take when on Wegovy can help you think through which of these are most relevant to your situation. For people following a plant-based diet, B12 supplementation is essential rather than optional.

What to avoid: megadose supplements marketed specifically at GLP-1 users. There's no robust clinical evidence that any proprietary blend designed for semaglutide users outperforms targeted standard supplementation based on your blood results. Save the money. For specific questions about vitamin D and its interaction with your treatment, our dedicated vitamin D and Wegovy page goes into more depth.

The semaglutide overview on our site explains how the medicine works and what to expect during treatment, which gives useful context for understanding why nutritional planning matters from the start. And if you're weighing up the practicalities of starting treatment, you can explore your treatment options or check your eligibility with our prescribers, the consultation is free and reviewed by a real clinician, not automated software.