Compounded Tirzepatide or Semaglutide "With B12" (or B6): What the Additive Does and Doesn't Do

The added B12, B6 or glycine does not have trial evidence behind it. No published human trial shows it reduces nausea or adds weight loss. FDA says adding B12 does not by itself stop a compounded product from counting as a copy of an approved drug¹. Lilly says its testing found an impurity in tirzepatide-B12 products².

Why is compounded tirzepatide sold "with B12" or "B6"?

Mostly to make it a different product on paper. Since the GLP-1 shortages ended, a compounding pharmacy may not regularly make what FDA calls "essentially a copy" of Zepbound or Wegovy. An extra ingredient gives the vial a different label, and sellers present it as a personalized formula. Some also say it helps with nausea or muscle loss.

Does adding B12 reduce nausea or help weight loss?

There is no human trial showing either. A PubMed search on October 9, 2026, found no trial in people that tested an added vitamin against the same GLP-1 without it.

The study sometimes cited is a 2020 animal study³. Researchers chemically bonded a B12 precursor to a GLP-1 drug, making a new molecule, and found fewer vomiting episodes in shrews. That is not the same as mixing B12 into a vial, and it was not tested in people.

What did Lilly's letter and FDA say about additive versions?

Lilly published an open letter in March 2026 saying its testing of compounded tirzepatide with B12 found an impurity formed when the two react⁴. A paper by Lilly scientists reported the impurity across samples from the U.S. market and said its clinical effects are unknown². Those are Lilly's findings, from the maker of Zepbound and Mounjaro, not an FDA finding.

FDA has addressed B12 directly. Its compounding guidance gives the example of semaglutide combined with vitamin B12: FDA may treat it as essentially a copy when it is given the same way and the amounts are within 10% of approved products¹.

Is "with B12" a different drug legally?

Not automatically. Under FDA's policy, what matters is whether a prescriber documents that the change makes "a significant difference" for that patient¹. An additive printed on every vial a seller ships is a different thing from a change made for one person. Our articles on whether compounded tirzepatide and semaglutide are still legal cover the rules in full.

Do sellers charge more for the B12 version?

Not where we can compare. EOS Health charges the same with or without its add-ons, and Goldspan Health charges the same for its B12 and glycine versions.

Who actually needs B12 supplementation?

People with a reason to run low, and a blood test tells you. Long-term metformin use is the best-known one: in a large diabetes prevention study, low or borderline-low B12 was about twice as common on metformin after five years (19.1% vs. 9.5%)⁵. A 2026 review of GLP-1 drugs flags B12 among the nutrients to watch, especially after weight-loss surgery, with stomach or bowel conditions, a poor diet, older age or long stretches of nausea and vomiting⁶. None of that requires B12 inside the GLP-1 vial.

For what is actually in a compounded vial, see what compounded tirzepatide is and what compounded semaglutide is. To compare sellers, see the tirzepatide and semaglutide boards, and which sellers say what pharmacy makes their drug.