Tirzepatide With B12 and Other GLP-1 Supplements

Tirzepatide with B12 is a compounded mix, not an FDA-approved drug, and no trial has tested it¹. Eli Lilly's testing found a significant impurity from a reaction between tirzepatide and B12, with unknown effects in people^{1, 2}.

If your vitamin B12 is low, a separate B12 supplement is the better-studied route³. Beyond B12, few supplements have been tested in people taking weight-management drugs; most advice is extrapolated from general weight-loss research⁴. This guide sorts what has evidence, what has none and what needs a prescriber first.

It is the medication tirzepatide mixed with a form of vitamin B12 by a compounding pharmacy, rather than an FDA-approved product. FDA does not review compounded drugs for safety, effectiveness or quality before they are marketed⁵.

A search of compounding sites in February and March 2025 found 33 unique semaglutide or tirzepatide products. Of those, 48% paired the drug with additives such as cyanocobalamin, glycine, niacinamide, docusate or ondansetron⁶.

Does Zepbound or Mounjaro have B12 in it?

No. Lilly states that tirzepatide has never been studied in combination with B12. The B12 versions come from compounders, telehealth companies and medspas¹.

Why do compounders add B12?

With the shortage of approved products over, compounding pharmacies can legally sell only products that differ from them, and extra ingredients are one way to differ⁶. Lilly says sellers market the mixes as "personalized" while adding the same untested additives to most products¹. A 2026 analysis of 33 such products found little justification for adding nutrients to injectable semaglutide or tirzepatide⁶.

For semaglutide, FDA notes that compounders add B12, B6, L-carnitine and NAD. It states that the safety and effectiveness of these combinations has not been established⁷.

Tirzepatide and Ozempic are similar in schedule but not in action. Both are once-weekly injections. Tirzepatide activates two receptors, GIP and GLP-1, while semaglutide (Ozempic, Wegovy) activates GLP-1 only^{8, 7}. The supplement questions below apply to both unless noted.

Its safety is unknown rather than proven harmful. The evidence is thin and comes mostly from the manufacturer of the approved drugs.

• The impurity: Lilly's tests of compounded tirzepatide-B12 samples found an impurity formed when tirzepatide reacts with certain B12 analogs. The paper describes it as widespread².
• What is unknown: Lilly says nothing is known about the impurity's short- or long-term effects, its toxicity, immune reactions or its effect on receptor binding¹. The paper likewise calls the clinical effects unknown².
• Reporting gaps: Lilly notes that compounders are not required to monitor or report adverse events¹.

As of May 31, 2026, FDA had received more than 730 adverse event reports for compounded tirzepatide and 990 for compounded semaglutide. Not all were B12 products, and FDA says these events are likely underreported and often resemble those of the approved drugs⁵.

What are the side effects of tirzepatide with B12?

Expect the side effects of tirzepatide itself. For Zepbound, Lilly lists nausea, diarrhea, vomiting, constipation, stomach pain, indigestion, injection site reactions, tiredness, allergic reactions, belching, hair loss and heartburn¹. The same summaries carry serious warnings: thyroid tumors, pancreatitis, gallbladder problems, severe stomach problems and vision changes in type 2 diabetes. Tirzepatide must not be used with a personal or family history of medullary thyroid carcinoma or with MEN 2¹. B12 adds little on its own: the National Academies set no upper limit for it because its toxicity is low³. The unknown part is the impurity.

How many units is my dose of tirzepatide?

There is no safe universal chart, because compounded vials come in different concentrations. FDA documented patients drawing 5 to 20 times the intended dose of compounded semaglutide, such as 50 units instead of 5⁷. FDA also received reports linked to compounded tirzepatide or semaglutide doses above the approved label⁵. Ask the dispensing pharmacy to write your dose in milligrams, milliliters and syringe units for your exact vial.

What color should tirzepatide with B12 be?

No label or regulator source we read sets an expected color, because each pharmacy formulates its own mix. FDA lists medicine that looks different from what you received before, or from what the seller pictured, as a warning sign. Other signs include prices that seem too good to be true and no licensed doctor available to answer questions⁵.

No evidence says it is. No trial compared the two, and Lilly says tirzepatide has never been studied with B12¹. The 2026 pharmacy review found little justification for the added nutrients⁶.

Sellers often imply B12 adds energy. NIH says B12 supplements do not appear to improve performance or endurance when B12 status is already adequate³.

Is B6 or B12 better with tirzepatide?

Neither has been shown to help. Lilly lists pyridoxine (B6), glycine, niacinamide and carnitine alongside B12 as additives with no proven clinical benefit for people taking tirzepatide¹. Our glycine page covers what that amino acid does in other settings.

Does B12 help with nausea from tirzepatide?

We found no study showing it does. The pharmacy review saw a rationale for adding ondansetron, an anti-nausea drug, but not for the nutrients. It found no evidence for ondansetron by subcutaneous injection⁶.

Take B12 if you are low or at higher risk, and check your level first. NIH names older adults, people with pernicious anemia or gut disorders, vegetarians, and anyone who has had stomach or weight-loss surgery as higher-risk groups³. GLP-1 drugs cut calorie intake, which can lead to nutritional deficiencies⁹. The evidence that they cause B12 deficiency specifically is weaker.

• Observational signal: a narrative review of six studies in 480,825 adults found thiamine and cobalamin deficits increased over time on GLP-1 drugs. The authors say causality cannot be established¹⁰.
• Tirzepatide trials: in the SURMOUNT-1 to 4 trials (4,726 participants), vitamin-deficiency adverse events occurred in 0.99% on tirzepatide and 1.07% on placebo. Vitamin levels were not routinely measured, so the trials cannot rule out a problem¹¹.
• Metformin: in a trial of 390 insulin-treated adults with type 2 diabetes, metformin 850 mg three times daily for 4.3 years cut B12 by 19% and raised the absolute risk of deficiency by 7.2 percentage points¹².

The metformin finding matters because some people take it alongside a GLP-1 drug. In the Diabetes Prevention Program follow-up, borderline-low or low B12 appeared in 19.1% of metformin users against 9.5% on placebo at 5 years¹³. Our summary of that study has the details.

Signs of low B12 are easy to miss. NIH lists fatigue, neurological changes, megaloblastic anemia, a sore tongue, palpitations and low blood counts. The body stores 1 to 5 mg, so symptoms can take years to appear³. The sources we read do not link low B12 to specific food cravings. See our B12 deficiency page and B12 for deficiency.

How much B12 and in what form?

NIH finds no evidence that absorption differs by form, such as cyanocobalamin or methylcobalamin³. The adult RDA is 2.4 mcg. B12-only supplements typically contain 500 to 1,000 mcg. Absorption is only about 2% at 500 mcg and 1.3% at 1,000 mcg, so a higher dose absorbs a smaller share³. Deficiency is usually treated with prescription injections. A Cochrane review of 3 trials in 153 people found oral doses of 1,000 to 2,000 mcg normalized levels about as well, though the evidence was low quality³.

The NIH fact sheet gives no time-of-day advice. It lists metformin and stomach-acid medicines as drugs that can lower B12 levels³. Our B12 food guide shows food sources.

Few supplements have been tested in people taking these drugs. Most advice comes from narrative reviews and expert panels, not supplement trials in GLP-1 users^{4, 9}.

The need is real in one respect. In a claims analysis of 461,382 adults starting a GLP-1 drug, 12.7% had a nutritional deficiency diagnosed within 6 months and 22.4% within 12 months. Vitamin D deficiency was the most common, at 7.5% and 13.6%¹⁴. People who saw a dietitian had more deficiencies recorded, which may reflect more testing. The data are observational, and most patients had type 2 diabetes¹⁴.

Lean mass is the other concern. In the SURMOUNT-1 body-composition substudy (160 adults, 72 weeks), tirzepatide cut weight by 21.3%, fat mass by 33.9% and lean mass by 10.9%. About 75% of the weight lost was fat and 25% lean mass, the same split as placebo¹⁵.

A 2025 narrative review of supplements during GLP-1 treatment suggests these options, drawing on obesity and weight-loss research more than GLP-1 trials⁴:

• Protein: supplements can help reach 1.2 to 2.0 g per kg of body weight daily⁴. If you have chronic kidney disease, check the target first: KDIGO advises avoiding more than 1.3 g per kg daily when the disease is at risk of progressing¹⁶. Our whey protein page covers the product.
• Whey with resistance training: the review says this combination helps preserve lean body mass during weight loss⁴.
• Multivitamin: recommended when intake is low or a deficiency is confirmed⁴.
• Fiber and probiotics: the review links them to better bowel regularity and fewer side effects⁴. See fiber and probiotics.
• Vitamin D and iron: test first. Vitamin D deficiency was diagnosed in 13.6% within a year¹⁴, and a review reported lower ferritin in GLP-1 users than in a comparison group¹⁰. See vitamin D and iron deficiency.

A joint advisory from four US nutrition and obesity societies puts food and exercise first: preventing nutrient deficiencies and preserving muscle and bone through resistance training and an adequate diet⁹. For foods that raise your own GLP-1, see GLP-1 foods. The tirzepatide trials counter the alarm somewhat. Malnutrition adverse events were rare: abnormal weight loss, underweight and low albumin each occurred in 0.06% or fewer of participants. A BMI below 18.5 was more frequent on tirzepatide, at 0.38% against 0.06% on placebo¹¹.

No trial has tested that combination in our searches, so there is no data on whether it helps or harms. Berberine is a much weaker weight-loss agent than these drugs, and it overlaps with them on side effects.

Is berberine like Ozempic?

No. The effects are not close, although the trials differ in population:

• Berberine, meta-analysis: 23 randomized trials found a 0.88 kg reduction in body weight (95% CI 0.39 to 1.36 kg) and a 0.48 kg/m² lower BMI¹⁷.
• Berberine, 6-month trial: in 337 adults with obesity and fatty liver, 1 g daily did not reduce visceral fat or liver fat versus placebo. It lowered LDL cholesterol by 7.72 mg/dL, and adverse events were similar between arms¹⁸.
• Tirzepatide: a 21.3% weight reduction at 72 weeks in the SURMOUNT-1 body-composition substudy, whose 160 adults had a mean starting weight of 102.5 kg¹⁵.

Berberine does lower blood sugar. A meta-analysis of 50 trials (4,150 participants) found it reduced fasting glucose by 0.59 mmol/L, and added to diabetes drugs it lowered HbA1c by a further 0.69%¹⁹. Our berberine page and berberine for weight loss go deeper, with a summary of the umbrella review.

What are the risks of stacking them?

• Gut effects: the umbrella review of 11 meta-analyses names constipation and diarrhea as berberine's common side effects²⁰. GLP-1 drugs share those effects¹. No study measured whether they add up.
• Low blood sugar: Lilly warns that low blood sugar risk rises when tirzepatide is used with insulin or a sulfonylurea¹. Because berberine also lowers glucose, anyone on those medicines should ask the prescriber first. That is our inference, not a tested interaction.
• Pregnancy and breastfeeding: MotherToBaby says berberine can pass into breast milk and may raise the risk of bilirubin buildup in a baby's brain²¹. Avoid it while breastfeeding and discuss it with a clinician if pregnant.

For prescription pills, mostly yes, with one clear exception. GLP-1 drugs slow gastric emptying, which can delay absorption of pills^{8, 22}. For vitamins and minerals, nobody has studied it.

• Tirzepatide's effect fades: it delayed emptying after a single dose, and the delay diminished after repeated doses in healthy volunteers. A residual delay remained in people with type 2 diabetes⁸.
• Most drugs are unaffected overall: a systematic review of 22 reports and 6 prescribing sheets found lower peak levels and later peaks with GLP-1 drugs. Total exposure did not change in a clinically meaningful way²². The reviewers urge caution with kidney dysfunction and narrow therapeutic index drugs²².
• Birth control pills: tirzepatide reduced oral contraceptive exposure in the one trial reviewed, which the other GLP-1 drugs did not²³. Lilly advises another method of birth control for 4 weeks after starting and after each dose increase¹.

We found no study of vitamin or mineral absorption on these drugs, so no timing rule is evidence-based. If you take levothyroxine, our guide on levothyroxine and supplements covers spacing.

We found no report of a harmful interaction, but no proof of benefit either. A 2026 commentary states that no randomized trial has tested creatine during GLP-1 weight loss²⁴. It calls the idea hypothesis-generating²⁴.

The case rests on creatine's known effect elsewhere. The 2025 supplement review lists creatine monohydrate as adding strength benefits when combined with resistance training⁴. See our creatine page, creatine for weight loss and mixing creatine with protein shakes.

Our literature search found no human data on ashwagandha or NAD+ taken with semaglutide or tirzepatide. That is an evidence gap, not a safety finding. Separately, NIH's LiverTox rates ashwagandha a likely cause of clinically apparent liver injury²⁵, so skip it if you have liver disease and call a clinician if you develop jaundice, dark urine or abdominal pain.

NAD is one of the additives FDA says compounders put into semaglutide products. FDA states the safety and effectiveness of such combinations has not been established⁷. Hair loss is also on Zepbound's list of common side effects¹; our hair health page covers the supplements studied for it.

These groups should check with a prescriber or pharmacist, based on Lilly's safety summaries¹:

• Insulin or sulfonylurea users: low blood sugar risk is higher with these medicines, so a glucose-lowering supplement adds uncertainty.
• Oral contraceptive users: the pills may work less well, and supplements do not change that.
• Pregnancy and breastfeeding: Zepbound may harm an unborn baby and may pass into breast milk, so tell a provider if you become pregnant or plan to breastfeed.
• Thyroid cancer history: do not use tirzepatide with a personal or family history of medullary thyroid carcinoma or MEN 2.
• Kidney disease: dehydration can harm the kidneys, and high protein targets may need adjusting (see the protein note above).
• Vomiting, diarrhea or dehydration: fluid loss may cause kidney problems, which matters before adding anything that changes fluid or electrolytes.
• Procedures with sedation: tell every provider you take the drug, because it may increase the chance of food entering the lungs.

People on long-term metformin should also ask about a B12 test¹².

Use these decision rules:

• Offered tirzepatide with B12? Ask whether the approved version is available. FDA says compounded drugs should only be used when an approved drug cannot meet the patient's need, and prescriptions should be filled at a state-licensed pharmacy⁵.
• Want B12? Ask for a blood level, especially on metformin, then supplement separately if low³.
• Worried about muscle? Put protein and resistance training first. Whey and creatine are add-ons: whey has support from weight-loss trials in general, and creatine has none yet during GLP-1 treatment^{4, 24}.
• Tempted by berberine, ashwagandha or NAD? Treat them as untested add-ons, and add one at a time so you can tell what changed.
• Have a problem? Report adverse events or quality issues to FDA's MedWatch program⁵.

Supplements in this guide

• Vitamin B12
• Berberine
• Creatine Monohydrate
• Whey Protein
• Vitamin D
• Fiber Supplements

We searched a research-paper index in several framings: compounded tirzepatide and B12, nutritional deficiencies on GLP-1 drugs, body composition, drug absorption, berberine, creatine, and metformin with B12. We read the PubMed abstracts of 18 journal records, and read seven web pages (Lilly's open letter, two FDA pages, the NIH B12 fact sheet, the KDIGO guideline summary, NIH LiverTox and MotherToBaby). All 25 are cited. The last three were added after an independent review.

We prioritized regulators, randomized trials and systematic reviews. The impurity paper comes from the maker of the approved drugs. We did not review an independent replication or the compounding industry's response. Most supplement advice rests on narrative reviews, and we found no trial of berberine, creatine, ashwagandha or NAD+ alongside a GLP-1 drug. Journal sources were read as abstracts, not full texts. Last researched October 29, 2026.

1. Eli Lilly and Company. An open letter from Eli Lilly and Company warning of potential patient safety risks associated with tirzepatide compounded with vitamin B12 (including the Zepbound and Mounjaro safety summaries). March 12, 2026. https://investor.lilly.com/news-releases/news-release-details/open-letter-eli-lilly-and-company-warning-potential-patient
2. Jordan B, et al. A novel, widespread impurity in mass-compounded tirzepatide/B12 products: potential patient safety implications. Expert Opin Drug Saf. 2026;25(5):837-845. doi:10.1080/14740338.2026.2663185
3. National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
4. Johnson BVB, et al. Dietary supplement considerations during glucagon-like Peptide-1 receptor agonist treatment: A narrative review. Obes Pillars. 2025;16:100209. doi:10.1016/j.obpill.2025.100209
5. U.S. Food and Drug Administration. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. https://www.fda.gov/drugs/drug-alerts-and-statements/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
6. Belcourt J, et al. Compounded Semaglutide and Tirzepatide Products Use Unique Formulations but Efficacy and Safety Largely Unknown. Ann Pharmacother. 2026;60(9):902-906. doi:10.1177/10600280261421979
7. U.S. Food and Drug Administration. FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products. https://www.fda.gov/drugs/human-drug-compounding/fda-alerts-health-care-providers-compounders-and-patients-dosing-errors-associated-compounded
8. Urva S, et al. The novel dual glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 (GLP-1) receptor agonist tirzepatide transiently delays gastric emptying similarly to selective long-acting GLP-1 receptor agonists. Diabetes Obes Metab. 2020;22(10):1886-1891. doi:10.1111/dom.14110
9. Mozaffarian D, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society. Am J Clin Nutr. 2025;122(1):344-367. doi:10.1016/j.ajcnut.2025.04.023
10. Urbina J, et al. Micronutrient and Nutritional Deficiencies Associated With GLP-1 Receptor Agonist Therapy: A Narrative Review. Clin Obes. 2026;16(1):e70070. doi:10.1111/cob.70070
11. Almandoz JP, et al. Nutritional status with tirzepatide in obesity: A post hoc analysis of the SURMOUNT-1-4 randomized clinical trials. Obes Pillars. 2026;17:100248. doi:10.1016/j.obpill.2026.100248
12. de Jager J, et al. Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency: randomised placebo controlled trial. BMJ. 2010;340:c2181. doi:10.1136/bmj.c2181
13. Aroda VR, et al. Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab. 2016;101(4):1754-61. doi:10.1210/jc.2015-3754 Our study summary.
14. Scott Butsch W, et al. Nutritional deficiencies and muscle loss in adults with type 2 diabetes using GLP-1 receptor agonists: A retrospective observational study. Obes Pillars. 2025;15:100186. doi:10.1016/j.obpill.2025.100186
15. Look M, et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight. Diabetes Obes Metab. 2025;27(5):2720-2729. doi:10.1111/dom.16275
16. KDIGO CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease (Executive Summary), Practice Point 3.3.1.1. https://kdigo.org/wp-content/uploads/2017/02/KDIGO-2024-CKD-Guideline-Executive-Summary.pdf
17. Elahi Vahed I, et al. The effect of berberine on obesity indices: a systematic review and meta-analysis. Int J Obes (Lond). 2026;50(1):53-73. doi:10.1038/s41366-025-01943-x
18. Lei L, et al. Berberine and Adiposity in Diabetes-Free Individuals With Obesity and MASLD: A Randomized Clinical Trial. JAMA Netw Open. 2026;9(1):e2554152. doi:10.1001/jamanetworkopen.2025.54152
19. Wang J, et al. Effects of administering berberine alone or in combination on type 2 diabetes mellitus: a systematic review and meta-analysis. Front Pharmacol. 2024;15:1455534. doi:10.3389/fphar.2024.1455534 Our study summary.
20. Li Z, et al. Berberine and health outcomes: An umbrella review. Phytother Res. 2023;37(5):2051-2066. doi:10.1002/ptr.7806 Our study summary.
21. MotherToBaby. Berberine. In: MotherToBaby Fact Sheets. Brentwood (TN): Organization of Teratology Information Specialists. https://www.ncbi.nlm.nih.gov/books/NBK600384/
22. Calvarysky B, et al. Drug-Drug Interactions Between Glucagon-Like Peptide 1 Receptor Agonists and Oral Medications: A Systematic Review. Drug Saf. 2024;47(5):439-451. doi:10.1007/s40264-023-01392-3
23. Skelley JW, et al. The impact of tirzepatide and glucagon-like peptide 1 receptor agonists on oral hormonal contraception. J Am Pharm Assoc (2003). 2024;64(1):204-211.e4. doi:10.1016/j.japh.2023.10.037
24. Ostojic SM, et al. Creatine for glucagon-like peptide-1-associated muscle loss. Clin Nutr. 2026;66:106805. doi:10.1016/j.clnu.2026.106805
25. National Institute of Diabetes and Digestive and Kidney Diseases. Ashwagandha. In: LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. https://www.ncbi.nlm.nih.gov/books/NBK548536/