Semaglutide with B12
Compounded semaglutide with cyanocobalamin
Written by Aaron CuhaReviewed Sep 2026
Also known as: Semaglutide/cyanocobalamin, Sema B12, Semaglutide with vitamin B12
In plain English, from Aaron
This is how I would explain it to a friend. The evidence, with the numbers, is further down the page.
This is compounded semaglutide with vitamin B12 mixed in. The pitch is that the B12 helps with the nausea and the tiredness. Here is what actually happens. The B12 is set by your semaglutide dose, not by your B12 level. So it goes up every time you titrate, whether you need it or not.
What people take it for
- Losing weight.
- Less nausea from the shot.
- More energy.
- Some people believe B12 helps the drug work. Nobody has tested that.
What the trials actually showed
Nobody has tested this mix. The semaglutide half is one of the best studied drugs on this site. In the STEP 1 trial, people lost 14.9 percent of their body weight in 68 weeks. The dummy shot group lost 2.4 percent. Half the drug group lost 15 percent or more. Nausea and diarrhoea were the main side effects. No vitamin was in that trial. The B12 half also has real trials, for a different job. In people with a proven B12 shortage, both pills and shots got over 90 percent of them back to normal in eight weeks. That is treating a shortage found by a blood test. Nobody has tested giving B12 to a person whose level is fine. Now the math, and it is odd. The B12 is held at 0.5 mg per mL no matter what. The semaglutide is either 1 mg per mL or 5 mg per mL. On the strong one, a 0.5 mg dose is 50 micrograms of B12. A 2.4 mg dose is about 240. On the weak one, that same 0.5 mg dose carries 250 micrograms. Five times the B12 for the same semaglutide.
What people report
Reports, not trial results
The good
- Hunger goes quiet.
- Weight comes off.
The bad
- Nausea. It is the main report on any semaglutide, and it does not look smaller on the B12 versions.
- Constipation and reflux.
- Feeling tired early on, which people often blame on the drug when they are simply eating far less.
- Most people say they cannot tell the B12 versions apart from the plain ones.
- Dose confusion, because the same milligram number is a different volume on the two strengths.
Where these come from: The nausea and diarrhoea numbers come from the trial side effect tables. The comparison between B12 and plain versions comes from patient forums and is just people talking.
My bottom line
The semaglutide is the real thing. The B12 is along for the ride at a dose set by something that has nothing to do with your B12. If you want to know whether you need B12, the test costs almost nothing.
An opinion, not a finding. I am a coach, not a doctor.
Overview
A compounded premix in which the B12 dose is decided by the semaglutide dose rather than by anyone's B12 level. Cyanocobalamin sits at 0.5 mg/mL across strengths while semaglutide is 1 or 5 mg/mL, so the same product delivers five times more B12 per milligram of semaglutide on one strength than on the other. No trial has tested the combination, and no trial supports the reason it is added.
Compounding pharmacies pair semaglutide with cyanocobalamin and the stated reasons are that B12 helps with the nausea and with the fatigue people report on a GLP-1. Neither claim has a trial behind it. What is true is that adding a vitamin to a peptide changes the preparation into something that is not a copy of an approved product, which has mattered to compounders for regulatory reasons at various points since the shortages ended.
The arithmetic is the part worth reading twice, because it is genuinely strange. Across the common compounded strengths, cyanocobalamin is held constant at 0.5 mg/mL while semaglutide is supplied at either 1 mg/mL or 5 mg/mL, in 1 mL and 2.5 mL vials. On the 5 mg/mL preparation, a 0.5 mg semaglutide dose is 0.1 mL, which carries 50 micrograms of B12. Titrate to 2.4 mg and the dose is 0.48 mL, which carries about 240 micrograms of B12. On the 1 mg/mL preparation, that same 0.5 mg of semaglutide is 0.5 mL and carries 250 micrograms of B12: five times as much B12 for identical semaglutide.
So three things follow that no label states. First, the B12 amount is a function of the semaglutide dose, so it rises every time you titrate, and it has no relationship to your B12 status. Second, two people on the same semaglutide dose from two different strengths receive five-fold different B12. Third, a person starting at 0.25 mg on the concentrated preparation receives 25 micrograms of B12 a week, which is a trivial amount by any standard for someone who actually needs B12.
The semaglutide half is one of the best documented drugs in this database. In STEP 1, mean body weight fell 14.9% at week 68 against 2.4% on placebo, an estimated treatment difference of 12.4 percentage points, with 50.5% of the semaglutide group losing 15% or more against 4.9% on placebo. Nausea and diarrhoea were the most common adverse events. None of that evidence involved cyanocobalamin.
The B12 half is also well documented, for a different thing entirely. In a randomised non-inferiority trial in primary care, oral and intramuscular B12 both normalised serum B12 in well over 90% of deficient patients at eight weeks. That is replacement therapy in people with a deficiency, identified by a blood test. It says nothing about giving B12 to someone whose level is normal.
Mechanism of action
Semaglutide is a GLP-1 receptor agonist that slows gastric emptying and reduces appetite through central and peripheral GLP-1 signalling. Cyanocobalamin is a vitamin B12 form used to correct deficiency, and its physiological effects in a person who is not deficient are minimal. There is no mechanistic account of why B12 would reduce GLP-1 nausea, and no trial has tested that claim.
Human evidence
The GLP-1 has large randomised trials, B12 replacement has randomised trials, and the combination has none.
- The premix: no published study, no registered trial of semaglutide co-formulated with B12.
- Semaglutide 2.4 mg weekly: 14.9% mean weight loss against 2.4% on placebo at 68 weeks in STEP 1.
- B12 replacement: normalises serum B12 in over 90% of deficient patients by eight weeks, oral or injected.
- The nausea claim: no trial has tested whether B12 reduces GLP-1 gastrointestinal side effects.
- The fatigue claim: no trial has tested B12 against GLP-1 associated fatigue in people with normal B12.
What this does not tell you: Two well-evidenced things in one syringe is not one well-evidenced thing. The half that works for weight is the half that was trialled without a vitamin, and the half that works for deficiency was trialled in people who had been tested and found deficient.
What it has been measured to do
Measured in people
Goals Semaglutide with B12 has been measured for in a human being, most people first. Counts come from the study lines on this page and deliberately undercount.
- Losing weightno headcount stated · 1 study
- Gut and digestionno headcount stated · 1 study
What people using it report
Uncontrolled and self-selected, so it cannot show that anything works. It is still the best guide on this page to what people actually do with Semaglutide with B12, what they expect, and what goes wrong. The full account, including the negative reports, is below.
33 of the 36 indexed goals have no study of any kind behind Semaglutide with B12
No trial, no animal work, no cell work on this page reports a result for these. That is an absence of evidence rather than evidence of absence, but it does mean anything you have been told about Semaglutide with B12 and one of these did not come from a study cited here.
Reading the research record
The honest reading is that the B12 is doing regulatory and marketing work more than physiological work. Adding an ingredient makes the preparation something other than an exact copy of the approved drug, which has mattered for what compounders may lawfully produce, and B12 has a reputation for energy that sells well. For a person who is genuinely B12 deficient, this is a fine way to get some B12 while it lasts, though the amount is set by an unrelated variable and rises as the semaglutide is titrated.
There is one real safety signal in this area, and it comes from the other incretin. Laboratory testing of compounded tirzepatide plus B12 products found a widespread impurity formed by a chemical reaction between the peptide and certain B12 analogues. That work was done by the manufacturer of the branded tirzepatide, a conflict that should be stated and weighed rather than used to dismiss it, and it tested tirzepatide rather than semaglutide. It is nonetheless the only published chemistry on premixing an incretin peptide with B12, and it found a reaction.
The evidence, charted
Fig. 1a · evidence scale
2human studies cited, participant count not stated
participants not stated
No participant total is drawn, because none of the human citations on this page gives one. Read the citations below for what each study measured.
Participant counts are read from the citation lines on this page. Where a line states no number, nothing is counted for it rather than estimated.
Fig. 1b · evidence mix
2 of 4 citations here are human work, the rest are not.
- Human · given to people250%
- In vitro · cells, tissue or a dish125%
- Review · summarises other work125%
Counted from the citation list on this page, typed as this page types it. It understates any literature larger than the sources we cite, and a review counts once however many studies it covers.
Fig. 2 · evidence over time
Evidence spans 3 distinct years, 2020 to 2026, counted from the citation list on this page.
Fig. 3 · legal status at a glance
US
Not approved
UK
Not approved
AU
Not approved
CA
Not approved
Not approved in any of the four jurisdictions shown. A jurisdiction's classification is a regulatory fact, not a verdict on the science; see Legal status below for the full text and any notes.
Fig. 5 · molecular identity
- Modality
- Blend
- Molecular weight
- Not on file
- Half-life
- Stated in words, not a number
- Sequence length
- None on file
see the exact wording below
Half-life as stated on file: Not defined for the mixture. The incretin component supports weekly dosing and the vitamin behaves as a vitamin, with no pharmacokinetic study of the combined preparation.
No amino acid sequence is on file for Semaglutide with B12, which is expected: a blend is not built from residues.
Fig. 6 · what is in the vial
No mass split can be drawn for this blend
Sellers do not publish a consistent vial size for Semaglutide with B12, so the share of each component is not knowable from the outside. Splitting the bar evenly would invent the number this page exists to question.
- Semaglutideamount not stated
- Cyanocobalaminamount not stated
Component list from the product labels we hold. Amounts are label mass, never a dose.
Key studies & citations
- Human2021
Once-Weekly Semaglutide in Adults with Overweight or Obesity
STEP 1. Mean body weight changed by 14.9% with semaglutide 2.4 mg weekly against 2.4% with placebo at week 68, an estimated treatment difference of 12.4 percentage points. 50.5% of the semaglutide group lost 15% or more of body weight against 4.9% on placebo. Nausea and diarrhoea were the most common adverse events, usually transient and mild to moderate. Semaglutide alone; no vitamin was co-administered.
New England Journal of Medicine - Human2020
Oral versus intramuscular administration of vitamin B12 for vitamin B12 deficiency in primary care: a pragmatic, randomised, non-inferiority clinical trial (OB12)
In patients with documented B12 deficiency, both oral and intramuscular B12 normalised serum concentrations in well above 90% of patients at eight weeks, with the between-arm difference at that point under 1% by per-protocol analysis. This is what B12 evidence looks like: replacement in people shown by a blood test to be deficient.
BMJ Open - Review2026
FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss
FDA's standing statement on compounded and other unapproved GLP-1 products, covering adverse event reports, dosing errors and the fact that compounded preparations are not reviewed by the agency for safety, effectiveness or quality.
FDA - In vitro2026
A novel, widespread impurity in mass-compounded tirzepatide/B12 products: potential patient safety implications
Analytical testing of compounded incretin plus B12 products from multiple US market sources identified a previously unidentified impurity arising from a chemical reaction between the peptide and certain B12 analogues. The work was performed and authored by Eli Lilly employees, which is a disclosed and relevant conflict, and it is the only published chemistry on peptide plus B12 premixes. The samples tested were tirzepatide products, not semaglutide.
Expert Opinion on Drug Safety
What users report
Self-reported experiences, not evidence. Nothing below was measured under controlled conditions, and reports like these cannot separate a real effect from placebo, from the training or diet change that accompanied it, or from what the product actually contained. They are here because knowing what people describe, including what goes wrong, is worth reading alongside the studies.
- Nausea, which is the dominant report on any semaglutide preparation and is not obviously less on the B12 versions.
- Constipation and reflux.
- Fatigue early in a cycle, which people often attribute to eating far less rather than to the drug.
- No perceived difference between the B12 and non-B12 versions, which is the most common comparison report.
- Confusion about dose, because the same milligram figure means different volumes on the 1 and 5 mg/mL strengths.
Sources: Trial adverse event tables supply the nausea and diarrhoea figures. The comparison between B12 and non-B12 preparations comes from forums including r/Semaglutide and telehealth patient communities, and is uncontrolled.
Frequently asked questions
Does the B12 help with nausea?
No trial has tested that. It is the reason given for the combination and it has no controlled evidence behind it.
How much B12 am I getting?
It depends on your semaglutide dose and your strength. Cyanocobalamin is held at 0.5 mg/mL, so on a 5 mg/mL semaglutide preparation a 0.5 mg dose carries 50 micrograms of B12 and a 2.4 mg dose carries about 240 micrograms. On a 1 mg/mL preparation, that same 0.5 mg dose carries 250 micrograms.
Is that a sensible B12 dose?
It is not a dose set by anything about you. It is set by how much semaglutide you happen to be taking that week, and it goes up every time you titrate. If you want to know whether you need B12, the test costs very little.
Is the combination approved?
No. Compounded preparations are not FDA approved and are not reviewed for safety, effectiveness or quality. Semaglutide itself is approved; this mixture is not.
Is there a chemistry problem with mixing a peptide and B12?
There is at least one published finding. Testing of compounded tirzepatide plus B12 products found a widespread impurity formed by a reaction between the peptide and certain B12 analogues. That testing was done by the branded manufacturer, which is a real conflict of interest, and it examined tirzepatide rather than semaglutide.