At a glance
- No standard semaglutide plus B12 dosage chart exists. The B12 amount and the semaglutide concentration are set by each compounding pharmacy, so the only valid chart is one built from your own vial label.
- On a combined vial the B12 dose is locked to the semaglutide dose: draw twice the volume and you get twice the B12. That makes unit conversion errors matter twice.
- The label titration in the STEP 1 trial runs 0.25, 0.5, 1.0, 1.7 and 2.4 mg weekly, stepping up every four weeks. Your prescriber's plan can differ.
- Evidence that GLP-1 drugs cause B12 deficiency is observational and a causal link is unproven. The firm evidence is for metformin, which matters if you take both.
- Injected B12 has no demonstrated advantage over oral B12 for most people with dietary deficiency, and weight-loss claims for B12 itself are not supported by the trials cited here.
Searching for a semaglutide B12 dosage chart returns a wall of near-identical pages, many of them auto-generated and several with garbled numbers. The reason is simple: no single chart can be correct. Semaglutide plus B12 is a compounded product, and each pharmacy chooses its own semaglutide concentration and its own cyanocobalamin amount. The correct chart is the one you build from the label on the vial in your hand.
This guide gives you the method and a worked example. It then covers what the research says about adding B12 to a GLP-1 regimen, which is thinner than the marketing suggests. For the underlying drug, see our semaglutide profile and the semaglutide dosage chart.
Why there is no universal semaglutide B12 chart
Branded semaglutide pens are standardized: each pen delivers a fixed dose, and the number on the dial is milligrams. A compounded vial is a different object. The pharmacy decides how many milligrams of semaglutide sit in each milliliter, and whether to add B12 and how much. Two vials from two pharmacies can both say "semaglutide with B12" while needing very different syringe volumes for the same 0.5 mg dose.
Quality also varies. A 2024 analysis of follow-on GLP-1 products found different impurity patterns from the originators, including high molecular weight species and residual solvents. That study examined generic follow-on products rather than compounded vials, so it does not tell you how a given compounded vial performs. A 2025 provider-facing review of compounded semaglutide points to the same practical problem: weaker quality controls than branded drugs and a real risk of dosing errors. Our compounded semaglutide reviews cover how we assess vendors.
The takeaway for dosing is that a chart downloaded from a random site cannot know your concentration. Treat any such chart as a template, never as an instruction.
The label titration schedule behind most charts
Most charts copy the escalation used for branded semaglutide at the weight-management dose. In the STEP 1 trial, adults with overweight or obesity and no diabetes started at 0.25 mg once weekly and stepped up every four weeks through 0.5, 1.0 and 1.7 mg to a 2.4 mg maintenance dose, with mean weight loss around 14.9% at 68 weeks versus around 2.4% on placebo. The trial tested branded semaglutide. It did not test compounded or B12-containing products, so its results do not transfer automatically to them.
| Weeks | Weekly dose (mg) | Notes |
|---|---|---|
| 1 to 4 | 0.25 | Starting dose, not a therapeutic dose |
| 5 to 8 | 0.5 | |
| 9 to 12 | 1.0 | |
| 13 to 16 | 1.7 | |
| 17 onward | 2.4 | Maintenance dose in STEP 1 |
Clinicians often slow this down or hold at a tolerated dose, particularly when nausea is a problem. The table is the trial schedule, not a prescription. Our GLP-1 dosing comparison shows how it sits next to tirzepatide.
How to build your own chart from the vial label
You need two numbers from the label: the semaglutide concentration (mg per mL) and the B12 concentration (mcg per mL, or mg per mL). If either is missing, ask the pharmacy before drawing a dose. Then work through three steps.
- Volume to draw (mL) = target dose in mg divided by semaglutide concentration in mg per mL.
- Syringe units = volume in mL times 100, on a standard U-100 insulin syringe where 100 units equals 1 mL.
- B12 delivered (mcg) = volume in mL times B12 concentration in mcg per mL.
The worked example below uses a hypothetical vial. It is arithmetic, not a recommendation. Substitute your own label values.
| Weekly dose | Volume (mL) | U-100 units | B12 delivered if label says 500 mcg/mL |
|---|---|---|---|
| 0.25 mg | 0.10 | 10 | 50 mcg |
| 0.5 mg | 0.20 | 20 | 100 mcg |
| 1.0 mg | 0.40 | 40 | 200 mcg |
| 1.7 mg | 0.68 | 68 | 340 mcg |
| 2.4 mg | 0.96 | 96 | 480 mcg |
Hypothetical vial: semaglutide 2.5 mg per mL, cyanocobalamin 500 mcg per mL. Only the semaglutide concentration affects units for a given dose; the B12 column simply follows.
Two things stand out in that table. First, at 2.4 mg the example vial needs 96 units, which is nearly a full 1 mL syringe, so a pharmacy that wants patients to inject smaller volumes will usually dispense a more concentrated vial. Second, B12 climbs in a fixed ratio with semaglutide. Someone who holds at a low dose gets little B12, and someone at the top dose gets nearly ten times as much as at the starting dose. If you want a particular B12 intake independent of your GLP-1 dose, a combined vial cannot deliver it.
Check the arithmetic against our reconstitution calculator if your product arrives as powder, and keep vial and syringe type consistent. Errors at this step are common enough to be studied: a study of adults using grey-market semaglutide without a prescription found that participants completed only 15 of 34 preparation and injection steps correctly in testing, including errors that could cause wrong dosing. Our semaglutide reconstitution chart walks through the powder-vial version.
Does adding B12 to semaglutide help?
The honest answer is that nobody has tested the combination. No randomized trial in our searches compared semaglutide with B12 against semaglutide alone. What exists is indirect.
GLP-1 drugs and nutritional status. A narrative review of micronutrient deficiencies with GLP-1 therapy notes that findings come mainly from observational data and that causality cannot be established. Proposed routes are lower food intake, slower gastric emptying and altered absorption. A case report of acute nutritional neuropathy during semaglutide treatment described low thiamine, folate and B12 in a patient with significant GI intolerance, with improvement after supplementation. One case shows a possible pathway. It does not show how common the problem is.
Metformin is the stronger signal. The randomized evidence on B12 loss points at metformin rather than GLP-1 drugs. A placebo-controlled trial of long-term metformin in type 2 diabetes reported lower B12 and higher homocysteine in the metformin group. The Diabetes Prevention Program Outcomes Study analysis linked longer metformin exposure to higher odds of B12 deficiency, and a 2014 systematic review of metformin-treated patients found lower B12 concentrations versus control. Many people on semaglutide also take metformin, so a low B12 in that group may reflect the metformin more than the semaglutide.
Injected or oral? For dietary deficiency, a randomized trial in megaloblastic anemia found oral cobalamin worked as well as intramuscular, and a systematic review of oral and nasal B12 in gastrointestinal disease reached a similar view except for patients with severe neurological signs. Injection stays standard where absorption is impaired. A small B12 dose bundled into a weekly semaglutide injection therefore has no demonstrated edge over a daily oral supplement.
Weight loss. None of the studies above show B12 itself speeding weight loss. The pitch that the B12 "boosts energy" or "reduces fatigue" on semaglutide is marketing language we could not tie to trial data.
Evidence and practical limits at a glance
| Question | Best available evidence | Strength |
|---|---|---|
| Does semaglutide with B12 outperform semaglutide alone? | No trial found | None |
| Do GLP-1 drugs cause B12 deficiency? | Observational data, narrative reviews, one case report | Weak, causality unproven |
| Does metformin lower B12? | Randomized trial, DPPOS analysis, systematic review | Moderate to strong |
| Is oral B12 adequate for dietary deficiency? | Randomized trial, systematic review | Moderate |
| Is a compounded vial dosed like a branded pen? | Quality and dosing-error literature | Not interchangeable |
What to do with this
Ask the pharmacy for the semaglutide concentration and the B12 amount in writing, and have your prescriber confirm the unit count for each step. If you take metformin, have B12 measured rather than assuming a bundled dose covers you; our lab testing guide lists what to request. If your only reason for the B12 add-on is nutritional insurance during rapid weight loss, an oral supplement chosen with your clinician may do the same job without tying B12 to your GLP-1 dose.
If you are weighing providers, we compare telehealth options in our Bodybuilding Health+ review and our Yucca Health review, and the cheapest semaglutide without insurance guide ranks the price lanes. For people on the research-peptide side who are comparing injectables, our Ascension Peptides review explains how we audit that vendor and the ENHANCED code applies there. Our GLP-1 telehealth page lists current prescriber partners, since semaglutide itself is a prescription drug.
The disclaimer
This article is for research and educational purposes only. It is not medical advice, a prescription, or a dosing instruction. The vial values in the tables are hypothetical examples. Semaglutide is a prescription medication, and any dose, schedule or supplement decision should be made with a licensed clinician who can read your actual vial label and medical history.
