# Supplements and Lab Tests on a GLP-1: Which Vitamins Help, What to Skip, What to Check

> Most people on a GLP-1 do not need a long supplement list. Guidelines back targeted help: a protein shake if you regularly miss protein, a fiber supplement for constipation, a multivitamin if you eat under about 1,200 kcal a day or meet other ADA criteria, and vitamin D, B12 or iron when your situation or labs call for it. Tell your lab about high-dose biotin.

- URL: https://glpcalendar.app/blog/supplements-and-labs-on-glp-1
- Published: 2026-09-29
- Updated: 2026-09-29
- Publisher: GLP Calendar (https://glpcalendar.app)

GLP-1 medicines such as semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) cut how much you eat, which raises fair questions about vitamins, supplements and blood work. The short version: a few supplements have guideline support in specific situations, many popular ones do not, and one common hair supplement can distort lab results. Here is what the evidence says and what to ask your clinician.

## Do GLP-1 medications cause vitamin deficiencies?

They can make them more likely, mainly because you eat less. In a large US insurance-claims study, 12.7% of adults starting a GLP-1 received a new nutrient-deficiency diagnosis within 6 months and 22.4% within 12 months, most often vitamin D. The study was observational and funded by Abbott, which sells nutrition products.

Key details from that study (Butsch et al., 2025):

- It followed 461,382 adults who started a GLP-1 between 2017 and 2021. Most (80.5%) had type 2 diabetes, and the most common drugs were dulaglutide, semaglutide and liraglutide.
- Vitamin D deficiency was diagnosed in 7.5% at 6 months and 13.6% at 12 months. Nutritional anemia, the most common deficiency-related complication, reached 2.1% and 4%.
- Compared with matched people taking metformin alone, differences appeared mainly at 12 months, notably for thiamine (vitamin B1) and vitamin D.

Read these numbers with care. They are diagnosis codes from insurance claims, not lab-confirmed rates, and the main analysis had no comparison group of non-users, so the study cannot show that the drug caused a deficiency. People who saw a dietitian had more deficiencies recorded, which the authors say may partly reflect more chances to detect them. Eight of the ten authors were Abbott employees; the other two worked under contract with the company.

As of September 2026, none of the major guidelines reviewed here asks for a routine lab panel for everyone on a GLP-1. The 2025 joint advisory suggests extra testing before treatment only for people with a history of very-low-calorie diets, bariatric surgery, celiac or other inflammatory disease, or a previous deficiency.

## Which supplements have evidence on a GLP-1?

Only a handful have guideline support, each for a specific situation: protein supplements when you fall short, fiber for constipation, a multivitamin for certain groups, vitamin D, B12 or iron when needed, and fluids with electrolytes on sick days. Most of the evidence below comes from people who are not taking GLP-1s.

The tiers: **A** means a guideline mentions it for a specific situation, **B** means reasonable but with indirect evidence, and **C** means weak or no evidence. Check every item with your clinician or pharmacist, especially if you take other medicines or have kidney disease.

| Tier | Supplement | When it may fit | Why |
|---|---|---|---|
| A | Protein shake or oral nutrition drink | You regularly miss your protein target | ADA 2026 encourages protein supplements as needed |
| A | Fiber supplement, such as psyllium | Constipation or low fiber despite food changes | Listed in the joint advisory; add slowly with fluids |
| A | Multivitamin-mineral | Under ~1,200 kcal/day, strict vegetarian, over 50, poor absorption, cutting food groups, or excessive weight loss | ADA 2026 criteria |
| A | Vitamin D, with or without calcium | Low intake or a low blood level | Joint advisory: consider for at-risk nutrients |
| A | Vitamin B12 | Long-term metformin, vegan diet, older age | ADA flags long-term metformin; strict vegetarians and over-50s are on its multivitamin list |
| A | Iron | Only a deficiency confirmed by blood tests | Iron is on the ADA screening list; do not guess |
| A | Oral rehydration solution | Vomiting or diarrhea days | Labels warn fluid loss can injure the kidneys |
| B | Creatine | Only with regular strength training | About 2.6 kg more lean mass across 4 trials in older adults; no GLP-1 trials |
| B | Magnesium, such as citrate | Constipation that fiber and fluids have not fixed | Mentioned in the joint advisory; ask a clinician first |
| B | Ginger or peppermint tea | Nausea | Expert suggestion in the joint advisory |
| C | HMB, BCAA or leucine pills | Not a muscle strategy | Did not add muscle mass on top of strength training in older adults |
| C | Collagen as your main protein | Top-up only | No trials show it protects muscle on a GLP-1 |
| C | Biotin for hair | Avoid high doses | No trials in GLP-1 hair shedding; high doses skew lab tests |
| C | GLP-1 booster or weight-loss supplements | Not recommended | ADA: supplements are not recommended for weight loss (grade A) |

Two notes on the evidence. The creatine figure comes from a 2021 meta-analysis of older adults in which creatine was the only add-on to strength training that increased lean mass. The HMB and BCAA finding comes from a 2026 meta-analysis of 9 trials in older adults with sarcopenia (age-related muscle loss): amino-acid products improved some strength and function measures, with low certainty, but not muscle mass. For protein and fiber amounts, see our [protein, fiber and water guide](https://glpcalendar.app/blog/glp-1-protein-fiber-water).

## Do you need a multivitamin on Zepbound or Ozempic?

Not automatically. The ADA's 2026 Standards of Care say a multivitamin-mineral supplement can be considered if you eat under 1,200 kcal a day, leave out nutrient-rich food groups, are a strict vegetarian, have a condition that impairs absorption, are over 50, or lose weight excessively.

The joint advisory adds that vitamin D, calcium and B12 can be considered proactively, tailored to the person. A multivitamin does not replace testing: if you have symptoms of a deficiency, ask whether specific levels should be checked.

The ADA also sets a trigger for testing. People with significant weight loss (more than 20% of starting weight) or rapid loss (more than 4% a month) should be screened for micronutrient deficiencies. The ADA's list of nutrients of concern includes iron, calcium, magnesium, zinc and vitamins A, D, E, K, B1, B12 and C. There is no universal schedule; your clinician decides what to check.

## Can biotin mess up your blood test results?

Yes. High-dose biotin, common in hair, skin and nail supplements, can make some lab tests read falsely high or falsely low. The FDA has warned about this since 2017 and says it has kept receiving reports of falsely low troponin results, a test used to diagnose heart attacks.

Guidance from the lab-medicine society ADLM (formerly AACC) fills in the details:

- **Which tests.** Many immunoassays can be affected, including thyroid tests (TSH, free T4), troponin and, depending on the lab's equipment, several tests on a typical GLP-1 panel: vitamin D, vitamin B12 and ferritin.
- **Which doses.** Biotin in multivitamins (up to 1 mg) has not been reported to interfere. High-dose supplements (5 mg or more) can.
- **How long to wait.** People who took 5–10 mg should wait at least 8 hours before a blood draw. Some tests may need up to 72 hours. People prescribed very high doses (100 mg a day or more) should stop for at least 72 hours unless that is medically inadvisable, which is a decision for their prescriber.
- **Kidney disease.** Biotin may stay higher for longer when kidney function is reduced.

The FDA page does not set a waiting period; its message is that clinicians and labs need to know. Tell whoever orders your blood work, and the lab, about every supplement you take. If a result does not match how you feel, ask whether biotin could explain it. A tracker such as GLP Calendar keeps your supplement schedule next to your lab results and shows a biotin reminder before a blood draw.

## Why does hair fall out on a GLP-1, and what helps?

Hair shedding is a label-listed side effect tied to weight loss, and it is usually temporary. On the Zepbound label, hair loss was reported in 4–5% of people versus 1% on placebo, far more often in women (7.1%) than men (0.5%), and no tirzepatide-treated patient stopped treatment because of it.

The American Academy of Dermatology describes this pattern, called telogen effluvium. Heavy shedding is common after losing 20 pounds or more, usually shows up a few months after the trigger, and stops as the body readjusts. Hair tends to regain its normal fullness within 6–9 months.

Shedding can also signal a gap in your diet. The joint advisory lists excessive hair loss among possible signs of nutrient deficiency, along with unusual fatigue, muscle weakness, poor wound healing and unusual bruising. So the first steps are to check your protein intake and ask whether iron studies (ferritin) and a complete blood count make sense. High-dose biotin is rarely the answer and complicates your labs. For how shedding fits the wider side-effect timeline, see [GLP-1 side effects week by week](https://glpcalendar.app/blog/glp-1-side-effects-timeline).

## Which blood tests should you get on a GLP-1?

There is no universal GLP-1 lab schedule. Guidelines use triggers instead: the ADA suggests screening for micronutrient deficiencies after more than 20% total weight loss or more than 4% a month, the Zepbound label calls for kidney checks when vomiting or diarrhea could lead to dehydration, and people with diabetes follow the ADA's routine schedule.

| Test | When it is suggested | Why it matters |
|---|---|---|
| Vitamin D (25-hydroxy) | After more than 20% total or 4% monthly loss, or if at risk; in diabetes, yearly "as appropriate" | Most common new deficiency code in claims data |
| Vitamin B12 | Metformin for more than 5 years (first visit, then yearly); after large or fast weight loss | On the ADA list of nutrients of concern |
| Ferritin, iron studies, complete blood count | After large or fast weight loss, or with fatigue or hair loss; CBC yearly in diabetes | Nutritional anemia was the top deficiency complication |
| Creatinine and eGFR (kidney function) | With vomiting or diarrhea that could dehydrate you, especially when starting or raising a dose | Dehydration can cause acute kidney injury |
| A1C (diabetes) | At follow-up visits if not done in the past 3 months | Tracks glucose control |
| Urine albumin-to-creatinine ratio and eGFR (diabetes) | Yearly | Kidney screening |
| Lipid panel (diabetes) | At the first evaluation; may be rechecked after medicine changes that affect it | Heart risk |
| Thiamine (vitamin B1) | Prolonged vomiting, very poor intake or very fast loss | Deficiency can cause Wernicke encephalopathy |
| Calcitonin | Not routine | The Zepbound label calls routine calcitonin monitoring of uncertain value |

These are the tests guidelines name, not a panel to order yourself. Reference ranges differ between labs, so ask your clinician to interpret results in context, and see our [tirzepatide guide](https://glpcalendar.app/blog/tirzepatide) for the medication itself.

## When is vomiting or not eating an emergency?

When it goes on for days, or when confusion, eye-movement problems or unsteadiness appear. A 2026 systematic review found six published cases of Wernicke encephalopathy, a brain emergency caused by thiamine (vitamin B1) deficiency, after semaglutide for obesity. All followed prolonged stomach symptoms and substantial weight loss.

The cases are rare, but outcomes were poor in several, including Korsakoff syndrome (lasting memory damage) and death. The review's authors stress that early thiamine given by injection or IV is essential, which is why this needs a hospital, not a supplement at home.

Get emergency care if, after days of vomiting or eating very little, you or someone you live with notices:

- confusion or trouble thinking clearly;
- abnormal eye movements, double vision or drooping eyelids;
- unsteady walking or loss of coordination.

MedlinePlus lists these as symptoms of Wernicke-Korsakoff syndrome and advises going to the emergency room if they appear. The Zepbound label also says to tell your healthcare provider right away about nausea, vomiting or diarrhea that does not go away, and to call right away for severe stomach pain that will not go away.

## What to do next

1. List every supplement you take, with doses, and share it with your prescriber and pharmacist.
2. Ask whether you meet the ADA criteria for a multivitamin, and whether vitamin D, B12 or iron testing makes sense for you.
3. Check the biotin dose in any hair, skin or nail product, and tell the lab before blood draws.
4. Ask about micronutrient labs if you have lost more than 20% of your starting weight, or more than 4% in a month.
5. Agree on a sick-day plan for vomiting or diarrhea: fluids, whether an oral rehydration solution suits you, and when to call.
6. If you take a GLP-1 pill, ask your pharmacist how to time supplements around it; our [semaglutide guide](https://glpcalendar.app/blog/semaglutide) covers the pill rules.
7. Seek urgent care for confusion, eye-movement problems or unsteadiness after days of vomiting or poor intake.

## Frequently asked questions

### Should I stop taking biotin before a blood test?

Ask the clinician who ordered the test first. Lab-medicine guidance from ADLM says people who took 5–10 mg should wait at least 8 hours before a blood draw, some tests may need up to 72 hours, and multivitamin-level biotin (up to 1 mg) has not been reported to interfere.

### Will a multivitamin stop hair loss on a GLP-1?

No trial has shown that. Shedding on GLP-1s is linked to weight loss and usually settles within months, so checking your protein intake and iron levels with your clinician is more useful than adding high-dose hair supplements.

### Is creatine safe to take with Zepbound or Ozempic?

Creatine has not been studied in people taking GLP-1s. In older adults it added a small amount of lean mass when combined with strength training, so it only makes sense alongside regular training and after checking with your clinician, particularly if you have kidney problems.

### Do supplements that claim to boost GLP-1 work?

There is no good evidence that they do. The ADA's 2026 Standards of Care give a grade A recommendation against nutritional supplements for weight loss because none has been shown to be effective.

### How often do I need blood work on tirzepatide?

There is no single schedule. Your clinician will usually base it on your conditions and on triggers such as diabetes follow-up visits, weight loss of more than 20% in total or more than 4% a month, or severe vomiting or diarrhea.

## Sources

- [Butsch et al., Nutritional deficiencies and muscle loss in adults using GLP-1 receptor agonists: retrospective claims study, Obesity Pillars, 2025 (funded by Abbott)](https://pmc.ncbi.nlm.nih.gov/articles/PMC12205620/)
- [American Diabetes Association, Standards of Care in Diabetes—2026, Section 8: Obesity and Weight Management](https://pmc.ncbi.nlm.nih.gov/articles/PMC12690172/)
- [American Diabetes Association, Standards of Care in Diabetes—2026, Section 4: Comprehensive Medical Evaluation (Table 4.1)](https://pmc.ncbi.nlm.nih.gov/articles/PMC12690184/)
- [ACLM, ASN, OMA and TOS joint advisory: Nutritional priorities to support GLP-1 therapy for obesity (Mozaffarian et al., Obesity Pillars, 2025)](https://pmc.ncbi.nlm.nih.gov/articles/PMC12264624/)
- [US Food and Drug Administration, Biotin interference with troponin lab tests (follow-up to the 2017 and 2019 safety communications)](https://www.fda.gov/medical-devices/in-vitro-diagnostics/biotin-interference-troponin-lab-tests-assays-subject-biotin-interference)
- [ADLM (formerly AACC), Guidance document on biotin interference in laboratory tests, 2020](https://myadlm.org/science-and-research/academy-guidance/biotin-interference-in-laboratory-tests)
- [Zepbound (tirzepatide), US prescribing information and Medication Guide, DailyMed, 2026](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=487cd7e7-434c-4925-99fa-aa80b1cc776b)
- [American Academy of Dermatology, Do you have hair loss or hair shedding?](https://www.aad.org/public/diseases/hair-loss/insider/shedding)
- [Bidesie and Oudman, Wernicke's encephalopathy following semaglutide treatment for obesity: systematic review, Obesity, 2026](https://pubmed.ncbi.nlm.nih.gov/42399213/)
- [MedlinePlus (US National Library of Medicine), Wernicke-Korsakoff syndrome](https://medlineplus.gov/ency/article/000771.htm)
- [Choi et al., Resistance training plus nutritional interventions in older adults: systematic review and meta-analysis, BMC Geriatrics, 2021](https://pubmed.ncbi.nlm.nih.gov/34772342/)
- [Xie et al., Resistance training plus amino acid-based supplements for sarcopenia: systematic review and meta-analysis, BMC Musculoskeletal Disorders, 2026](https://pubmed.ncbi.nlm.nih.gov/41540398/)

---

Educational content, not medical advice. GLP Calendar is a tracking app; it does not recommend or calculate doses.