GLP-1 weight loss medications like Ozempic and Mounjaro may cause vitamin and mineral deficiencies because they reduce food intake, slow stomach emptying, and cause nausea that makes eating harder. According to Gram Research analysis, people taking these drugs face increased risk of low iron, vitamin B12, vitamin D, calcium, and zinc levels, particularly those over 65, with prior stomach surgery, or experiencing ongoing nausea. Most deficiencies detected so far are mild, but doctors should monitor patients with regular blood tests and recommend targeted supplements.
Popular weight loss medications like Ozempic and Mounjaro work by reducing hunger and food intake, but according to Gram Research analysis, they may also lower your body’s ability to absorb important vitamins and minerals. A new clinical review examined how these drugs affect nutrient levels and found that people taking them—especially those who feel nauseous or have stomach problems—might develop deficiencies in iron, vitamin B12, vitamin D, calcium, and zinc. While most cases are mild, the research suggests doctors should monitor patients more carefully and recommend specific vitamin supplements during long-term treatment.
Key Statistics
A 2026 clinical review in Obesity Pillars identified five major nutrient risk domains—blood nutrients, fat-soluble vitamins, bone minerals, trace elements, and electrolytes—in patients taking GLP-1 receptor agonists and dual GIP/GLP-1 agonists for obesity treatment.
Iron and vitamin B12 deficiencies appear most concerning in GLP-1 users because these medications slow stomach emptying and reduce overall food intake, both of which impair nutrient absorption.
Patients at highest risk for micronutrient deficiencies during GLP-1 therapy include those over 65 years old, individuals with prior bariatric surgery, people with baseline gastrointestinal disorders, and those experiencing prolonged nausea and vomiting.
The 2026 review recommends individualized nutritional assessment and targeted laboratory monitoring for high-risk GLP-1 patients, though prospective studies are still needed to define optimal monitoring strategies and supplement protocols.
The Quick Take
- What they studied: How GLP-1 weight loss medications (like Ozempic and Mounjaro) affect your body’s ability to get and use vitamins and minerals from food
- Who participated: This was a review of existing research, not a new study with participants. Researchers looked at data from diet studies, patient records, clinical trials, and safety reports involving people taking these medications
- Key finding: People taking GLP-1 drugs may develop low levels of important nutrients like iron, B12, vitamin D, calcium, magnesium, and zinc because they eat less food, have stomach problems, and lose weight quickly
- What it means for you: If you’re taking a GLP-1 medication for weight loss, talk to your doctor about getting blood tests to check your vitamin levels and ask whether you need supplements. This is especially important if you feel sick to your stomach or have a history of stomach surgery
The Research Details
Researchers reviewed published studies, patient safety reports, and clinical trial data to understand how GLP-1 medications affect nutrient absorption and levels. They looked at the biological mechanisms—the ways these drugs work in your body—that might cause vitamin problems. The review combined information from multiple sources including dietary studies that measured what people actually eat, observational studies that tracked patients over time, laboratory research on how the stomach works, and reports of side effects from patients taking these medications.
The researchers identified several ways these medications might lower nutrient levels: people eat much less food overall, they may avoid certain foods due to nausea or stomach discomfort, their stomach empties more slowly, and rapid weight loss can affect how the body stores and uses nutrients. They also looked at which patients might be at highest risk, including older adults, people with previous stomach surgery, and those with poor diet quality before starting the medication.
Understanding these risks matters because GLP-1 medications are now prescribed to millions of people for weight loss, and long-term use could lead to serious health problems if nutrient deficiencies aren’t caught and treated. By reviewing all available evidence together, researchers can help doctors create better monitoring plans and help patients avoid complications like anemia, bone weakness, or nerve damage from vitamin deficiencies.
This is a narrative review, meaning researchers read and summarized existing studies rather than conducting a new experiment. This type of review is useful for identifying patterns and gaps in knowledge, but it’s not as strong as a controlled trial. The findings are based on current evidence, which is still limited—most reported nutrient problems are mild or detected only through blood tests, not causing obvious symptoms yet. The researchers were careful to note that more research is needed to understand how common these problems really are and how serious they might become.
What the Results Show
The review identified five main areas where nutrient problems might occur: blood-related nutrients (especially iron and B12), fat-soluble vitamins (A, D, E, K), bone-related minerals (calcium and vitamin D), trace elements (zinc, copper, selenium), and electrolytes (magnesium, potassium). Iron and B12 deficiencies appear most concerning because these medications slow stomach emptying and reduce food intake, both of which make it harder for the body to absorb these nutrients.
Vitamin D and calcium deficiencies are also important because rapid weight loss can affect bone health, and people taking these drugs may avoid dairy products due to stomach problems. Zinc deficiency could affect immune function and wound healing. Most of the nutrient problems reported so far are detected through blood tests and don’t cause obvious symptoms yet, but the researchers warn that serious complications could develop in people who take these medications for many years.
The review found that certain groups are at higher risk: people over 65, those who had weight loss surgery before, people with stomach or digestive disorders, those with poor nutrition before starting the medication, and anyone experiencing ongoing nausea or vomiting. These high-risk patients may need more frequent blood tests and targeted supplements.
Additional concerns include thiamine (vitamin B1) deficiency, which can cause nerve damage if severe, and folate deficiency, which affects cell division and DNA. Potassium imbalances could affect heart rhythm in susceptible people. The review also noted that the severity of nutrient problems depends on how much weight someone loses, how long they take the medication, and how much their eating habits change. People who maintain good nutrition despite reduced appetite may have fewer problems than those who eat very little or avoid whole food groups.
These findings parallel what doctors learned from weight loss surgery, where nutrient deficiencies are a known complication requiring lifelong monitoring. However, GLP-1 medications work differently than surgery—they don’t physically remove part of the stomach—so the pattern and severity of deficiencies may differ. Previous research on other appetite-suppressing medications didn’t show these same nutrient concerns, suggesting that the specific way GLP-1 drugs affect the stomach and digestion creates unique risks. The review suggests that GLP-1 medications may carry higher nutrient risk than previously recognized.
This review has important limitations: it’s based on existing studies that weren’t designed to specifically track nutrient levels in GLP-1 users, so data is incomplete. Most reported cases are mild or found only through blood tests, making it unclear how many people actually develop serious problems. The review doesn’t include long-term data because these medications haven’t been used widely for many years yet. Different studies measured nutrients differently, making comparisons difficult. The review couldn’t determine exact rates of deficiency because studies used different methods and followed patients for different lengths of time. Finally, most evidence comes from people taking these drugs for weight loss rather than for diabetes, so results may not apply equally to both groups.
The Bottom Line
High confidence: People taking GLP-1 medications should have baseline blood tests before starting treatment and periodic monitoring (every 3-6 months initially) to check iron, B12, vitamin D, calcium, and magnesium levels. Moderate confidence: High-risk patients (older adults, those with prior stomach surgery, poor baseline nutrition, or ongoing nausea) should receive targeted supplements and more frequent monitoring. Low to moderate confidence: All patients should be counseled to maintain diverse, nutrient-rich foods despite reduced appetite and to consider a multivitamin supplement. Prospective studies are needed to establish optimal monitoring schedules and supplement recommendations.
Anyone taking GLP-1 medications (Ozempic, Mounjaro, Saxenda, Wegovy) for weight loss or diabetes should discuss nutrient monitoring with their doctor. This is especially important for people over 65, those with a history of stomach surgery, people with digestive disorders, and anyone experiencing persistent nausea. People with excellent baseline nutrition and no stomach problems may have lower risk but should still be monitored. Those taking these medications short-term (under 1 year) may have lower risk than long-term users, but monitoring is still recommended.
Nutrient deficiencies typically develop gradually over months to years, not immediately. Most people won’t notice symptoms early because mild deficiencies don’t cause obvious problems. However, some nutrients like B12 can become depleted within 6-12 months in susceptible people. Iron deficiency may develop within 3-6 months in people with poor baseline iron stores. Vitamin D deficiency may take 6-12 months to develop. This is why regular blood testing is important—it catches problems before they cause symptoms like fatigue, weakness, or bone pain.
Frequently Asked Questions
Can GLP-1 weight loss drugs like Ozempic cause vitamin deficiencies?
Yes, research shows GLP-1 medications may cause deficiencies in iron, B12, vitamin D, calcium, and zinc by reducing food intake, slowing stomach emptying, and causing nausea. Most cases are mild, but regular blood testing is recommended, especially for people over 65 or with prior stomach surgery.
What vitamins should I monitor if I’m taking Mounjaro or Ozempic?
Priority nutrients include iron, vitamin B12, vitamin D, calcium, magnesium, and zinc. Ask your doctor about baseline blood tests before starting medication and periodic monitoring every 3-6 months. Consider a multivitamin supplement, especially if you experience nausea or eat limited food variety.
How long does it take to develop vitamin deficiency on GLP-1 medications?
Deficiencies typically develop gradually over months to years. B12 may deplete within 6-12 months in susceptible people, iron within 3-6 months if baseline stores are low, and vitamin D within 6-12 months. Regular blood testing catches problems before symptoms appear.
Who is at highest risk for nutrient problems with GLP-1 drugs?
Higher-risk groups include people over 65, those with prior weight loss surgery, individuals with digestive disorders, people with poor baseline nutrition, and anyone experiencing persistent nausea or vomiting. These patients need more frequent monitoring and targeted supplements.
What symptoms suggest I have a vitamin deficiency from GLP-1 medication?
Watch for fatigue, weakness, shortness of breath (iron deficiency), tingling in hands/feet (B12 deficiency), bone pain (vitamin D/calcium deficiency), or frequent infections (zinc deficiency). Report these to your doctor immediately—blood tests can confirm deficiencies before symptoms become serious.
Want to Apply This Research?
- Log weekly: (1) nausea/stomach symptoms on a 1-10 scale, (2) food variety score (number of different food groups eaten daily), (3) appetite level, and (4) any symptoms of deficiency (fatigue, weakness, tingling, pale skin). Set reminders for scheduled blood tests and supplement doses.
- Create a ’nutrient-dense foods’ list within the app featuring iron-rich foods (lean meat, beans, fortified cereals), B12 sources (eggs, dairy, fortified plant-based products), calcium sources (dairy, leafy greens, fortified alternatives), and vitamin D sources (fatty fish, egg yolks, fortified milk). Set daily reminders to eat at least one food from each category despite reduced appetite. Track supplement adherence with daily check-ins.
- Set calendar reminders for blood work every 3-6 months. Create a nutrient tracking dashboard showing test results over time with normal ranges highlighted. Generate alerts if results trend toward deficiency. Track symptom patterns (fatigue, weakness, tingling) and correlate with test results. Share reports with healthcare provider quarterly to adjust supplements as needed.
This article summarizes a clinical review of existing research and is for educational purposes only. It is not medical advice. GLP-1 medications are prescription drugs that should only be used under medical supervision. If you are taking or considering GLP-1 medications, consult your healthcare provider about your individual nutrient risk, appropriate blood testing, and supplementation needs. Do not start, stop, or change any medication or supplement without medical guidance. This review identifies potential risks based on current evidence, but long-term safety data is still being collected. Individual responses to these medications vary significantly.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.