Micronutrient Gaps on GLP-1 Drugs: What to Monitor (Ozempic, Wegovy, Mounjaro)
GLP-1 drugs work by making you eat far less, and eating less food means taking in fewer vitamins and minerals — so real micronutrient gaps can open up over months of treatment. The evidence points to a few specific ones to watch: vitamin D is the most common deficiency, iron stores (ferritin) tend to fall, and calcium, B12, and thiamine intakes often run low. The sensible response is not to panic-buy a cabinet of pills but to keep your protein and overall diet quality high, take a basic foundation like vitamin D and a standard multivitamin, and ask your clinician to check the relevant labs rather than guessing.
The whole mechanism of semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) is appetite suppression and slowed gastric emptying — you feel full sooner and eat much less. That is exactly why they work for weight loss, but it is also why they can quietly create nutrient shortfalls: when total food intake drops by hundreds of calories a day for months, the vitamins and minerals that ride along with that food drop too. Most people will be fine, but a meaningful minority develop measurable deficiencies, and a few of them matter. Here is what the current evidence actually flags.
What the data show
A 2026 narrative review in Clinical Obesity pulled together six studies covering more than 480,000 adults on GLP-1 receptor agonists and found a consistent pattern [1]. Vitamin D deficiency was the most common abnormality, present in about 7.5% of users at six months and 13.6% at twelve months. Iron depletion was frequent — GLP-1 users had roughly 26-30% lower ferritin (the marker of stored iron) than people taking a different diabetes drug class for comparison. More than 60% of users were eating below the estimated requirement for calcium and iron, and average vitamin D intake was only about 20% of the recommended amount. Deficits in thiamine (vitamin B1) and cobalamin (vitamin B12) tended to grow over time [1]. None of this proves the drug "causes" deficiency in a strict sense — most of the data are observational — but the direction is clear and mechanistically obvious: less food in, fewer nutrients in.
The ones worth watching
Vitamin D is the headline because it is both the most common gap and one many people are already low in before starting. A standard 1,000-2,000 IU/day is a reasonable foundation, with the dose guided by a blood level if your clinician checks one. Iron deserves attention especially in menstruating women, where falling ferritin can cause fatigue that is easy to blame on the diet alone; iron should be confirmed with a ferritin test before supplementing, since unnecessary iron is not benign. Vitamin B12 and calcium round out the list — B12 because intake of animal protein often falls, and calcium because dairy intake commonly drops while the bone stress of rapid weight loss rises. These are the four the literature keeps returning to.
How serious can it get
For most people the answer is "mild and correctable," but the tail of the distribution is real. A 2025 case report described a 39-year-old man on semaglutide (after a prior bariatric procedure) who developed severe leg weakness and an inability to walk, traced to thiamine and vitamin E deficiencies; stopping the drug and repleting the vitamins reversed much of the damage over a month [2]. That is an extreme, multi-factor case — the combination of bariatric surgery plus a GLP-1 drug stacks two appetite-suppressing interventions — but it illustrates why "I just am not hungry" is worth taking seriously rather than ignoring for a year. Neurological symptoms, unusual fatigue, or hair and nail changes are signals to get labs, not to push through.
A sensible approach
The goal is to cover the predictable gaps without turning a weight-loss plan into a supplement-stacking project. Three steps cover most of it. First, protect diet quality: with a smaller appetite, make the food you do eat nutrient-dense — protein, vegetables, dairy or fortified alternatives — rather than spending your limited calories on refined carbohydrate. Second, take a simple foundation: a standard multivitamin plus vitamin D handles the broad-spectrum risk cheaply, and is the one place where a routine supplement is genuinely justified here. Third, test rather than guess: ask your prescriber to check vitamin D, ferritin, and B12 (and thiamine if you have neurological symptoms) at intervals, and target supplementation to what is actually low. That is far more useful than buying a dozen single-nutrient bottles on spec.
Sources
- Urbina J, Salinas-Ruiz LE, Valenciano C, Clapp B. "Micronutrient and Nutritional Deficiencies Associated With GLP-1 Receptor Agonist Therapy: A Narrative Review." Clinical Obesity, 2026;16(1):e70070. PMID 41549912.
- Donigan EC, Ingersent E, Wanberg EJ, et al. "Severe lumbosacral polyradiculopathy secondary to micronutrient deficiencies in a patient on semaglutide therapy following bariatric surgery." Endocrinology, Diabetes & Metabolism Case Reports, 2025;2025(3):25-0072. PMID 40956288.
- Chavez AM, Carrasco Barria R, León-Sanz M. "Nutrition support whilst on glucagon-like peptide-1 based therapy. Is it necessary?" Current Opinion in Clinical Nutrition and Metabolic Care, 2025;28(4):351-357. PMID 40401903.