Tirzepatide or semaglutide with niacinamide, B12 or glycine: what the added ingredient does

The 30-second summary

• The extra ingredient is mostly about the law, not the medicine. After the US shortages ended, compounders could no longer sell plain copies, and many added something to make their product different.
• None of the add-ins has been shown to improve a GLP-1. A 2026 analysis found little justification for adding nutrients, and a 2026 lab study found a new impurity in tirzepatide and B12 products.
• Compounded is not the same as licensed. The FDA does not review compounded drugs for safety, effectiveness or quality, and in the UK the MHRA says powder vials are not authorised.

Why these combinations exist

While semaglutide and tirzepatide were officially in shortage, US compounding pharmacies were allowed to make their own versions of semaglutide and tirzepatide. Then the FDA declared the shortages over:

After that, compounders could not legally sell what amounted to copies of the approved medicines. As a 2026 analysis in the Annals of Pharmacotherapy puts it, they could only sell "unique" products: a different route or dose, or an added ingredient.

That analysis searched compounding websites in early 2025 and found 33 such products. About half combined semaglutide or tirzepatide with one or more of vitamin B12 (cyanocobalamin), glycine, niacinamide, the stool softener docusate or the anti-sickness medicine ondansetron. A 2024 study of the direct-to-consumer market in Colorado found similar combinations, including B vitamins, glycine and levocarnitine, sold by businesses that were most often medical spas or weight-loss services. In 41 of the 93 businesses it found, the website mentioned FDA approval when describing compounded products.

Adding an ingredient does not automatically take a product out of copy territory. The FDA says it may still consider a compounded product that combines semaglutide with another ingredient, such as vitamin B12, to be essentially a copy if it is given the same way and both ingredients are within 10% of the strengths of commercially available products.

What each add-in is, and the evidence

The Annals of Pharmacotherapy authors concluded they "found little justification for adding nutrients or docusate sodium" to injectable semaglutide or tirzepatide. For ondansetron, they saw a rationale, since nausea is common, but noted that evidence for giving it under the skin is lacking.

On the vitamins themselves, the NHS gives these limits for supplements:

• B12: 2 mg or less a day is unlikely to cause harm; there is not enough evidence on the effects of high daily doses. Adults need about 1.5 micrograms a day.
• Niacin: 500 mg or less a day of nicotinamide is unlikely to cause harm; there is not enough evidence on high daily doses.
• B6: taking 200 mg or more a day can cause loss of feeling in the arms and legs, and the effect of 10 mg to 200 mg a day is unclear.

Compounded products differ, so check the label for what is in yours and how much, and tell your prescriber.

Is it the same as Mounjaro or Wegovy?

No, and the differences matter.

• Not reviewed. The FDA says compounded drugs are not FDA-approved, and that it does not review them for safety, effectiveness or quality before they are marketed.
• Different ingredients. The FDA has warned about compounded semaglutide made with salt forms, such as semaglutide sodium and semaglutide acetate, which are different active ingredients from those in the approved medicines.
• Dosing errors and side effects. The FDA has received reports of adverse events, some requiring hospital treatment, that may be linked to dosing errors with compounded injectable semaglutide. As of 31 May 2026, it had received 990 reports of adverse events linked to compounded semaglutide and more than 730 linked to compounded tirzepatide.
• A new impurity. A 2026 study in Expert Opinion on Drug Safety tested compounded tirzepatide and B12 products bought in the US and found a widespread, previously unidentified impurity, formed by a chemical reaction between tirzepatide and certain forms of B12. Its clinical effects are unknown.

(See compounded semaglutide and tirzepatide and the FDA's action on compounded GLP-1s.)

B12 and GLP-1 medicines: the real question

There is a genuine nutrition issue here, just not the one the vial solves. A 2026 review of micronutrients during GLP-1 treatment lists vitamin B12 among the nutrients of most concern, alongside iron, vitamin D, calcium, magnesium and zinc, because people eat less and less varied food. Most problems reported so far were mild or picked up only on tests, and the risk was higher in people with previous weight-loss surgery, digestive problems, older age or long spells of nausea and vomiting.

The answer to that is food, and testing if you are at risk, not an injection mixed into your medicine. B12 is found in meat, fish, milk, cheese and eggs. If you are vegan, have had weight-loss surgery or have been unwell for a while, ask your prescriber whether your levels should be checked. (See nutrient gaps on a GLP-1 and vegetarian or vegan on a GLP-1.)

If you are in the UK

The MHRA's guidance, updated in February 2026, says:

• GLP-1 medicines supplied as a powder in vials, which must be mixed with liquid before injecting, are not authorised and pose significant health risks.
• They should not be bought from beauty salons, social media, or anywhere without a prior consultation with a healthcare professional.
• There have been reports of severe side effects from fake GLP-1 medicines, and of counterfeit pens that closely copy the real ones.
• You can check that a pharmacy in Great Britain is registered on the General Pharmaceutical Council website, or with the Pharmaceutical Society of Northern Ireland.

If you already use one

• Talk to a prescriber about switching to a licensed medicine. Take the vial or its label with you, so they can see exactly what you have been taking.
• Report side effects. In the UK, use the MHRA's Yellow Card scheme; in the US, tell your prescriber and the FDA.
• Get vitamins from food, or from a tested supplement your prescriber agrees to, rather than relying on what is in the vial.

What to do with this

What protects you on a GLP-1 is eating enough of the right things on a smaller appetite, not an ingredient mixed into the injection. The calculator works out your protein floor and calorie target.

Get your numbers

Sources

1. US Food and Drug Administration. FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize. fda.gov
2. US Food and Drug Administration. FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss. fda.gov
3. Belcourt J, et al. Compounded Semaglutide and Tirzepatide Products Use Unique Formulations but Efficacy and Safety Largely Unknown. Ann Pharmacother 2026. PubMed
4. Jordan B, et al. A novel, widespread impurity in mass-compounded tirzepatide/B12 products: potential patient safety implications. Expert Opin Drug Saf 2026. PubMed
5. DiStefano MJ, et al. Compounded glucagon-like peptide-1 receptor agonists for weight loss: the direct-to-consumer market in Colorado. J Pharm Policy Pract 2024. PubMed
6. Simancas-Racines D, et al. Micronutrient risk with GLP-1 receptor and dual incretin agonists in obesity. Obesity Pillars 2026. PubMed
7. NHS. Vitamin B. nhs.uk
8. Medicines and Healthcare products Regulatory Agency. GLP-1 medicines for weight loss and diabetes: what you need to know. gov.uk

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