Compounded semaglutide and tirzepatide are often sold with a second ingredient in the same vial. The usual four are vitamin B12, glycine, niacinamide and pyridoxine, which is vitamin B6.
The question here is narrow. What is each ingredient, why does a compounder add it, and what do FDA documents and published studies say about it? Cost is left out, and so is any comparison of sellers.
What the approved injections contain
The starting point is the approved product, because every added ingredient is a departure from it. The Wegovy label lists, for each 1 mL of its single-dose pen solution, “disodium phosphate dihydrate, 1.42 mg; sodium chloride, 8.25 mg; and water for injection” [1].
Its multi-dose pen swaps the salt for “phenol, 5.5 mg; propylene glycol, 14 mg” as inactive ingredients [1]. The Wegovy tablet lists only “magnesium stearate and salcaprozate sodium (SNAC)”.
The Zepbound label lists, for each single-dose pen or vial, “sodium chloride (4.1 mg), sodium phosphate dibasic heptahydrate (0.7 mg), and water for injection” [2]. Its multi-dose forms add benzyl alcohol, glycerin and phenol.
Neither label mentions B12, cyanocobalamin, glycine, niacinamide or pyridoxine anywhere in its text [1] [2]. Whatever these four ingredients do, the approved drug’s trials did not include them.
The regulatory reason an ingredient gets added
FDA declared the tirzepatide shortage resolved on December 19, 2024, and the semaglutide shortage on February 21, 2025 [3]. After that, pharmacies faced a limit that shortages had suspended.
FDA’s April 1, 2026 update restates it. A 503A pharmacy may not compound, “regularly or in inordinate amounts, any that are essentially copies of a commercially available drug product” [3].
The exception is written into the statute. A drug is not essentially a copy when there is “a change, made for an identified individual patient, which produces for that patient a significant difference, as determined by the prescribing practitioner” [4].
That is the opening an added ingredient appears to use. One 2025 study of compounded GLP-1 marketing said as much. It wrote that compounders may keep selling these products “so long as they are modified in some way to meet an individual patient need, for example by adding a B vitamin” [6].
FDA addressed that exact case. Its 2026 update says it “may consider a compounded drug product that combines semaglutide API and another API, such as vitamin B12 (cyanocobalamin), to be essentially a copy” [3].
Two conditions trigger that view. The products are given the same way, such as by injection, and “the amounts of semaglutide and vitamin B12 in the compounded drug product are within 10% of the strengths of the respective commercially available drug products” [3].
The 2018 guidance behind that update sets out what counts as documentation. It gives sample notes such as “No Dye X, patient allergy” and says a prescription naming only a patient and a formulation “would not be sufficient” [4].
It also rules out one reason entirely. Factors “such as a lower price, are not sufficient to establish that the compounded drug product is not essentially a copy” [4].
The guidance quotes Congress on pretext. Where a significant difference “is a mere pretext”, the compounding “would be considered copying of commercially available products” if done regularly or in inordinate amounts [4].
How often these products appear is measurable. A 2026 review found 33 compounded semaglutide or tirzepatide products that differed from the approved ones, identified online between February and March 2025. Of those, 48% combined the drug with cyanocobalamin, glycine, niacinamide, docusate or ondansetron [5].
An earlier survey of 93 businesses in Colorado, searched in spring 2024, found 8 advertising GLP-1 products compounded with B vitamins and 1 with glycine [6]. That was before either shortage ended.
For how compounding law treats peptides more broadly, see are peptides legal. The rest of this page takes each ingredient in turn.
Vitamin B12 (cyanocobalamin)
B12 is the most common of the four. Marketing for these combinations tends to present it as support for energy or weight loss. The Colorado survey described such additives as “claimed to bolster the drug’s impact on weight loss” [6].
No trial supports that claim for a combined injection. The best-known B12 evidence in a weight and diabetes population comes from a different drug, metformin.
In the Diabetes Prevention Program, 1,073 adults took metformin 850 mg twice daily and 1,082 took placebo for 3.2 years [7]. The metformin group then continued open-label for about 9 more years.
Low B12, defined as 203 pg/mL or less, occurred in 4.3% on metformin versus 2.3% on placebo at 5 years (P = .02) [7]. At 13 years the gap, 7.4% versus 5.4%, was not significant (P = .12).
Each year of metformin use carried an odds ratio of 1.13 for B12 deficiency (95% CI 1.06 to 1.20) [7]. The authors suggested routine B12 testing in people taking metformin.
That finding concerns metformin, which many people on a GLP-1 drug also take. It says nothing directly about semaglutide or tirzepatide.
For GLP-1 drugs themselves, a 2026 narrative review lists B12 among the micronutrients worth watching [8]. It traces the risk to eating less, a narrower diet, slower stomach emptying and prolonged nausea or vomiting.
The same review says most abnormalities reported so far are “subclinical or indirect” [8]. It calls for prospective studies to define how often they occur and how to monitor for them.
One small retrospective study adds a signal. In 29 Japanese adults with type 2 diabetes who took weekly semaglutide after sleeve gastrectomy, serum albumin, B12 and zinc fell only after semaglutide began [9].
Those were post-surgery patients, a group with its own absorption risks, and there was no control group. The result cannot be generalized to people who have not had surgery.
So a B12 question on a GLP-1 drug is a reasonable one to raise, especially alongside metformin or after bariatric surgery. Nothing published shows that B12 mixed into the injection is the way to answer it. The diet side is covered in what to eat on semaglutide.
Pyridoxine (vitamin B6)
Pyridoxine is usually presented as a nausea aid, since nausea is the most familiar side effect of these drugs. The evidence for B6 and nausea is real, but it comes from pregnancy.
In a 1991 double-blind trial, 59 pregnant women took pyridoxine 25 mg every 8 hours for 72 hours, or placebo [10]. Among those with severe nausea, the nausea score fell by 4.3 points on B6 against 1.8 on placebo (P < .01).
In mild to moderate nausea, and in the group as a whole, there was no significant difference [10]. After 3 days, 8 of 31 women on B6 had any vomiting, against 15 of 28 on placebo (P < .05).
A 1995 trial randomized 342 women at 17 weeks’ gestation or earlier to pyridoxine 30 mg a day or placebo for 5 days [11]. Nausea scores fell more on pyridoxine (p = 0.0008). The drop in vomiting episodes was not significant (p = 0.0552).
A 2015 Cochrane review pooled what it could from 41 trials in 5,449 women [12]. It found “only limited evidence” for vitamin B6 and other drugs in relieving mild or moderate nausea and vomiting of early pregnancy.
What is known about nausea on semaglutide, including how often it occurs and when it eases, is covered in Ozempic nausea.
Glycine
Glycine is the simplest amino acid. Marketing for tirzepatide or semaglutide with glycine commonly links it to keeping muscle during weight loss. Some descriptions call it a stabilizer instead.
Neither role has been measured for these products. No published study has tested glycine with semaglutide or tirzepatide, and the 2026 review of compounded products found “little justification for adding nutrients” to injected combinations [5].
The approved tirzepatide and semaglutide injections are stable without it, since neither label lists glycine [1] [2]. Muscle loss on GLP-1 drugs is a real question, and the trial data on it are set out in GLP-1 muscle loss.
Niacinamide
Niacinamide, also called nicotinamide, is a form of vitamin B3. It shows up most often in compounded tirzepatide.
It does have a history as an ingredient in an approved injection. The label for one fast-acting insulin lists “niacinamide, USP (20.8 mg)” per mL among its inactive ingredients [13].
That label does not say what the niacinamide is for [13]. It also says nothing about how niacinamide behaves in a vial with tirzepatide, a different peptide at a different strength.
No published study has tested niacinamide with tirzepatide or semaglutide. The 2026 review lists it among the added nutrients it found little justification for [5].
What mixing can change
An added ingredient is not only a question of benefit. It can change the product itself, and one 2026 analysis shows how.
Scientists employed by the maker of brand tirzepatide tested samples of compounded tirzepatide combined with B12, bought from several U.S. sources. They reported a widespread, previously unidentified impurity [14].
It came from a chemical reaction between tirzepatide and certain analogs of B12. The authors state that the clinical effects of this impurity are unknown [14].
The authors’ employer makes the competing approved drug, which is worth weighing. The chemistry is still the point: a test of the raw tirzepatide could not have shown a product formed in the mixture.
That is why a certificate of analysis for the finished mixture matters more than one for the starting powder, as explained in how to read a peptide COA.
FDA’s general position covers all four combinations. Compounded drugs “are not FDA approved”, and the agency “does not review compounded drugs for safety, effectiveness or quality before they are marketed” [15].
Questions worth asking a prescriber
If a prescription includes one of these ingredients, three questions follow from the documents above. None is a recommendation to start, stop or switch anything.
- What significant difference does the added ingredient make for me, and is it written on the prescription? The guidance expects that to be documented [4].
- Has my B12 level been checked, if I take metformin or have had bariatric surgery? That is where the published B12 signal is clearest [7] [9].
- Was the finished mixture tested, or only the starting ingredients? The tirzepatide and B12 impurity formed in the mixture [14].
For the side effects of the drug itself, measured in its own trials, see semaglutide side effects.