Can GLP-1 Medications Cause Vitamin Deficiency?

Yes, GLP-1 medications including semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) can raise the risk of vitamin and mineral deficiencies. The drugs suppress appetite, reduce total food intake, and may alter nutrient absorption in the digestive tract.

Not everyone on GLP-1 therapy will develop a deficiency. Risk is higher for people with already limited diets, frequent nausea or vomiting, a history of bariatric surgery, or older age. Always consult your doctor before making changes to your supplement routine.

Which nutrients are most at risk with GLP-1 medications?

The most commonly reported deficiency among GLP-1 users is vitamin D. A 2026 review in Clinical Obesity analyzing data from nearly 480,000 adults found 13.6% of participants had vitamin D deficiency after 12 months of GLP-1 treatment. The same review found iron depletion was also common, with GLP-1 users showing 26% to 30% lower ferritin levels than people taking other diabetes medications. A separate 2026 review in Obesity Pillars added that B vitamins (including B12 and folate), calcium, magnesium, zinc, and thiamine are also frequently low, especially in people who experience persistent nausea, vomiting, or severe appetite reduction. Harvard Health’s summary of the study data notes that anemia from nutritional deficiency affected 4% of GLP-1 users in the large cohort, and 2.6% had B vitamin deficiencies. In rare cases, severe thiamine deficiency can lead to Wernicke encephalopathy, a serious neurological condition, though this is very uncommon Clinical Nutrition, 2026.

Why do GLP-1 medications cause nutrient deficiencies?

There are three main mechanisms behind GLP-1-related nutrient gaps. First, appetite suppression leads to lower total food intake, so many people consume fewer vitamins and minerals overall even if they eat nutrient-dense foods Clinical Obesity, 2026. Second, delayed gastric emptying, a common side effect of GLP-1s, slows the movement of food through the digestive tract, which can reduce absorption of nutrients like iron and B12 that are absorbed in the upper small intestine Obesity Pillars, 2026. Third, rapid weight loss and gastrointestinal side effects like nausea or vomiting can further reduce nutrient intake and increase losses. People who had bariatric surgery before starting a GLP-1 are at even higher risk, as they already have altered nutrient absorption Obesity Pillars, 2026.

How can you reduce deficiency risk on GLP-1 medications?

Small, intentional changes to your diet and routine can lower your risk of deficiencies. First, prioritize nutrient-dense foods: since you are eating smaller portions, choose foods that pack more vitamins and minerals per bite, such as leafy greens, lean proteins, legumes, and fortified whole grains Obesity Pillars, 2026. Adequate protein intake is also critical to preserve muscle mass during weight loss; you can learn more about meeting your protein needs on GLP-1s here. Second, get regular blood work to check your nutrient levels. Your doctor can test for vitamin D, iron, B12, folate, and other key nutrients when you start a GLP-1, and repeat testing every 6 to 12 months to catch any gaps early Clinical Obesity, 2026. If you are diagnosed with a B12 deficiency, supplements with methylated B12 and folate are easier for the body to absorb, as explained here. Third, consider a targeted supplement if your diet is limited or your blood work shows low levels. For people who struggle to meet their nutrient needs through food alone, our Keel digestive enzyme and multivitamin formula includes methylated B12, folate, iron, zinc, magnesium, vitamin D3, and probiotics to support absorption, taken as two capsules a day.

The wider picture, with the calculators, is in our guide to eating and supplementing well on GLP-1 medications.

FAQ

Do all GLP-1 users develop nutrient deficiencies? No, not everyone on GLP-1 therapy will develop a deficiency. Risk is higher for people with already limited diets, frequent nausea or vomiting, a history of bariatric surgery, or older age Obesity Pillars, 2026. Which nutrient deficiency is most common with GLP-1 medications? Vitamin D deficiency is the most frequently reported, affecting up to 13.6% of users after 12 months of treatment, followed by iron deficiency and B vitamin deficiencies Clinical Obesity, 2026. Should I take a multivitamin while on a GLP-1 medication? Talk to your doctor before starting any new supplement. If your diet is limited or your blood work shows low levels of specific nutrients, a targeted supplement may help fill gaps, but high doses of some nutrients can cause side effects or interact with other medications. Can GLP-1 medications cause permanent nutrient deficiencies? Most deficiencies are reversible if caught early and treated with dietary changes or supplements. Severe, long-term untreated deficiencies can cause lasting health problems, so regular monitoring with your doctor is important Clinical Obesity, 2026.

Sources

• Study: Taking GLP-1 drugs may increase risk of key nutrient deficiencies [www.health.harvard.edu]
• Micronutrient and Nutritional Deficiencies Associated With GLP-1 Receptor Agonist Therapy: A Narrative Review [Clinical obesity, 2026 (Journal Article, Review)]
• Micronutrient risk with GLP-1 receptor and dual incretin agonists in obesity: Mechanistic pathways, clinical signals, and a monitoring framework [Obesity pillars, 2026 (Journal Article, Review)]
• Nutritional deficiencies and muscle loss in adults with type 2 diabetes using GLP-1 receptor agonists: A retrospective observational study [Obesity pillars, 2025 (Journal Article)]
• Medical nutrition in the glucagon-like peptide-1 (GLP-1) era: Protein strategies, micronutrient monitoring, and lean mass preservation [Clinical nutrition ESPEN, 2026 (Journal Article, Review)]
• Wernicke's Encephalopathy Following Semaglutide Treatment for Obesity: A Systematic PRISMA Review of Case-Based Evidence [Clinical nutrition (Edinburgh, Scotland), 2026 (Journal Article, Review)]

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