The most important vitamins to take with Mounjaro are vitamin D, iron, B vitamins, and calcium. Because Mounjaro significantly reduces your appetite, you’re eating less food overall, which means you’re also taking in fewer essential nutrients. A large review of over 480,000 adults on GLP-1 medications found that vitamin D deficiency was the most common nutritional problem, affecting 13.6% of users after 12 months. Iron deficiency hit 3.2%, B vitamin deficiency 2.6%, and 4% developed anemia from nutritional shortfalls.
Those numbers actually understate the problem. A smaller study that tracked the actual food intake of 69 GLP-1 users found that 72% consumed less than the recommended amount of calcium, 64% fell short on iron, and only 1.4% met vitamin D recommendations. When you’re eating smaller portions, getting adequate nutrition through food alone becomes genuinely difficult.
Start With a Daily Multivitamin
A standard daily multivitamin covers the broadest ground with the least effort. It won’t fully replace what you’re missing from reduced food intake, but it provides a baseline of vitamin D, B vitamins, iron, and other micronutrients that tend to drop during rapid weight loss. Harvard Health’s Dr. Robert Shmerling specifically recommends that people on GLP-1 medications consider a daily multivitamin, with particular attention to vitamin D, iron, and B vitamins.
That said, a multivitamin alone may not be enough for certain nutrients, especially if you’re losing weight quickly or your starting levels were already low. The supplements below address the specific gaps Mounjaro users are most likely to develop.
Vitamin D
Vitamin D deficiency is the single most common nutritional issue for people on GLP-1 drugs. Your body gets vitamin D from sunlight, fatty fish, fortified dairy, and eggs, but all the food sources become harder to hit when your appetite is suppressed. Most multivitamins contain 600 to 1,000 IU of vitamin D, which may be sufficient if your levels are normal to begin with. If bloodwork shows you’re already low, your provider may recommend a higher dose. Vitamin D3 is the preferred form because your body absorbs and uses it more efficiently than D2.
Calcium
Calcium and vitamin D work together to protect your bones, and both tend to drop when you’re eating less. The food diary study found nearly three-quarters of GLP-1 users weren’t getting enough calcium from their diet. This matters especially during weight loss, when your skeleton can lose density along with body fat. Aim for roughly 300mg of calcium per meal through a combination of food (dairy, leafy greens, fortified plant milks) and supplementation if needed. Calcium citrate is generally easier on the stomach than calcium carbonate, which is worth considering since Mounjaro can already cause digestive discomfort.
Iron and B Vitamins
Iron deficiency and anemia are the second-biggest nutritional concern on GLP-1 medications. If you’re eating less red meat, beans, and fortified grains, your iron intake drops quickly. Symptoms of low iron include fatigue, feeling cold, brain fog, and brittle nails. Women who menstruate are at higher risk. Taking iron with vitamin C (a glass of orange juice, for instance) improves absorption significantly, while taking it with calcium or coffee blocks it.
B vitamins, particularly B12 and folate, play roles in energy production and red blood cell formation. B12 deficiency can mimic iron-deficiency symptoms: fatigue, weakness, and difficulty concentrating. If you’ve also been on metformin for diabetes, your B12 risk is compounded, since metformin independently reduces B12 absorption. A B-complex supplement or a multivitamin with adequate B12 covers this gap.
Magnesium
Magnesium supports muscle function, blood sugar regulation, and digestion. All three of those are relevant on Mounjaro. Low magnesium can show up as muscle cramps, fatigue, or worsened constipation. Magnesium glycinate and magnesium citrate are the best-tolerated forms. Magnesium oxide, the cheapest option on store shelves, is poorly absorbed and more likely to cause loose stools. If you’re supplementing electrolytes, aim for around 50 to 100mg of magnesium per serving, or roughly 100mg per meal from food and supplements combined.
Electrolytes Beyond Magnesium
Reduced food intake means reduced electrolyte intake across the board. When you eat less, you naturally consume less sodium, potassium, and magnesium, and if Mounjaro causes nausea or vomiting early on, you lose even more. Signs of electrolyte imbalance include muscle cramps, headaches, dizziness, and fatigue that doesn’t improve with sleep.
You don’t necessarily need a dedicated electrolyte supplement. Salting your food, eating potassium-rich foods like bananas and avocados, and drinking bone broth can go a long way. If you do supplement, look for products with around 200 to 300mg sodium, 100 to 200mg potassium, and 50 to 100mg magnesium per serving. Coconut water is a reasonable natural alternative for potassium, though it won’t cover sodium.
Protein: The Nutrient That Matters Most
Protein isn’t a vitamin, but it’s the most important dietary priority on Mounjaro. When you lose weight rapidly, your body doesn’t just burn fat. It also breaks down muscle, and losing too much lean tissue slows your metabolism, weakens your bones, and makes it harder to keep weight off long-term. Research suggests aiming for 1.6 to 2.2 grams of protein per kilogram of body weight daily to preserve muscle. For a 200-pound person, that’s roughly 145 to 200 grams per day.
Hitting those numbers is hard when your appetite is suppressed. Prioritizing protein at every meal helps: eggs or Greek yogurt at breakfast, chicken or fish at lunch and dinner, and a protein shake to fill gaps. Many people on Mounjaro find it easier to drink protein than to eat it, especially during the first few weeks at a new dose.
Supplements for Hair Loss
Hair thinning is one of the more distressing side effects of rapid weight loss, regardless of the method. The medical term is telogen effluvium: when your body is under stress (including caloric restriction), it shifts hair follicles into a resting phase, and you notice increased shedding about two to three months later. It’s usually temporary, but nutritional deficiencies can make it worse and slow regrowth.
Biotin is the most commonly recommended supplement for this. In a study of women experiencing hair loss after bariatric surgery (a comparable rapid-weight-loss scenario), those who were biotin-deficient saw improvement with 1mg daily. Over-the-counter hair supplements typically contain 5 to 10mg of biotin per day. Zinc also supports hair growth and is commonly paired with biotin in hair-focused supplements. However, the evidence for biotin helping people who aren’t actually deficient is weak. Getting your levels tested before supplementing is the most useful step.
Digestive Support: Probiotics and Fiber
Mounjaro slows gastric emptying, which is how it reduces appetite, but it also means food sits in your stomach longer. This can cause bloating, nausea, and constipation. A multi-strain probiotic with at least 10 billion CFUs may help maintain healthy gut bacteria and improve digestion during treatment. Digestive enzyme supplements taken at the start of meals can also help your body break down the smaller, denser meals you’re eating.
Fiber is trickier. It supports digestive regularity and helps you feel full, but adding too much fiber when your stomach is already emptying slowly can worsen bloating and discomfort. If you supplement fiber, increase the dose gradually and drink plenty of water. Getting fiber from food (vegetables, berries, chia seeds) is generally better tolerated than large doses of powdered fiber supplements.
Timing and Interactions
A few practical notes on supplement timing. Iron and calcium compete for absorption, so take them at least two hours apart. Iron absorbs best on an empty stomach, though it can cause nausea, so taking it with a small amount of food is a reasonable trade-off. Fat-soluble vitamins (A, D, E, K) absorb better when taken with a meal that contains some fat. Magnesium is often best taken in the evening, since it has a mild relaxing effect that can help with sleep.
If you’re taking Mounjaro alongside other medications like metformin or thyroid drugs, spacing your supplements matters more. Some minerals can interfere with medication absorption when taken at the same time. Your pharmacist can help you map out a schedule that avoids conflicts.