What Are the Benefits and Risks of Tirzepatide Injectable with Glycine?
Tirzepatide injectable with glycine is a compounded weekly shot that puts tirzepatide and glycine in the same vial. It is not FDA-approved, and SURMOUNT-1 results do not automatically apply to this mix. Eli Lilly's March 2026 letter named glycine as an untested add-in.
Written for Dominia Health education · Reviewed by Ariel Bowerman, BSN, R.N. · Last evidence check: September 2026
Tirzepatide injectable with glycine is a compounded weekly shot that puts tirzepatide and glycine in the same vial. It is not FDA-approved. Labeled FDA-approved tirzepatide (Zepbound, Mounjaro) does not contain glycine. SURMOUNT-1 weight-loss results at 5–15 mg do not automatically apply to this mix. Eli Lilly's March 12, 2026 open letter named glycine as one of several untested add-ins used in mass-compounded tirzepatide.
Last evidence check: September 2026. No dedicated randomized trial of tirzepatide plus same-vial glycine has been published, at standard or microdose strengths.
This page covers injectable tirzepatide with glycine, including the lower-dose "microdose" version (Microdose option: what's different). For the B12 mix, see tirzepatide injectable with B12.
What "With Glycine" Means
Glycine is an amino acid sold as a supplement and used in some IVs. Putting it in the same sterile syringe as tirzepatide is a compounding choice, not an FDA-reviewed combination. Ingredient evidence ≠ combination evidence.
What Is in the Vial
A compounded vial is intended to contain tirzepatide plus glycine. Strengths vary by pharmacy. Approved pens use set milligram doses and start at 2.5 mg weekly. Do not convert internet "units." Multi-dose vials raise sterility questions after the first puncture.
Why Clinics Add Glycine Instead of Giving It Separately
Marketing often claims glycine is "calming," helps sleep, or supports the mix. Those are separate glycine claims. They do not prove that same-vial glycine improves weight loss or makes tirzepatide safer.
What Is Proven vs. Unproven
| Item | FDA-approved tirzepatide | Compounded tirzepatide + glycine |
|---|---|---|
| Status | FDA-approved | Not FDA-approved |
| Typical weekly dose | Start 2.5 mg; maintain 5–15 mg | Varies by compounder; "microdose" vials usually below 2.5 mg |
| Weight-loss evidence | SURMOUNT-1: about 15–21% at 72 weeks at 5–15 mg | No dedicated RCTs of this mix |
| Glycine in same syringe | No | Yes; not FDA-reviewed |
| 2026 manufacturer signal | Not applicable | Lilly listed glycine among untested additives (March 12, 2026) |
SURMOUNT-1 (Jastreboff et al., NEJM, June 4, 2022): mean weight change at week 72 was −15.0% (5 mg), −19.5% (10 mg), and −20.9% (15 mg) versus −3.1% placebo. Those figures describe FDA-approved tirzepatide, not a compounded glycine vial.
Risks That Apply to Any Tirzepatide
Gastrointestinal effects were the main adverse events in SURMOUNT-1:
| Effect (SURMOUNT-1) | 5 mg | 10 mg | 15 mg | Placebo |
|---|---|---|---|---|
| Nausea | 24.6% | 33.3% | 31.0% | 9.5% |
| Diarrhea | 18.7% | 21.2% | 23.0% | 7.3% |
| Constipation | 16.8% | 17.1% | 11.7% | 5.8% |
| Vomiting | 8.3% | 10.7% | 12.2% | 1.7% |
| Stopped drug for an adverse event | 4.3% | 7.1% | 6.2% | 2.6% |
Serious labeled risks include pancreatitis, gallbladder disease, dehydration/kidney injury, hypoglycemia with certain diabetes drugs, and a boxed warning about thyroid C-cell tumors in rodents. Avoid with MTC or MEN2.
Risks Unique to Same-Vial Glycine
On March 12, 2026, Lilly warned about a tirzepatide–B12 impurity and separately said compounders also mix tirzepatide with glycine, B6, niacinamide, and carnitine — additives that "lack proven clinical benefits for tirzepatide patients and could create additional safety risks." That is a manufacturer warning about untested combinations, not a human trial of glycine + tirzepatide.
FDA states that compounded drugs are not reviewed for safety, effectiveness, or quality before marketing. Research-use-only vials are not recommended for human use.
Who Might Discuss This with a Prescriber
A clinician may discuss FDA-approved tirzepatide if you meet labeled criteria. Same-vial glycine is a different product. Do not use with MTC/MEN2, relevant allergy, or a research-only listing.
How This Differs from Zepbound or Mounjaro
Approved pens have no glycine in the device and use labeled milligram steps. Compounded "personalized" glycine mixes are not those pens, and compounded is not a generic.
Microdose Option: What's Different
A "microdose" tirzepatide-and-glycine vial is the same mix at a smaller, clinic-chosen amount, usually below the 2.5 mg weekly start on the approved label (which then rises toward 5, 10, or 15 mg). FDA does not define the term, and SURMOUNT-1 did not test that range for weight loss.
- Stacked unknowns: an add-in Lilly calls untested, at a dose no trial studied. No combination RCT exists for either strength.
- Same cautions: labeled tirzepatide risks, multi-dose-vial handling, and the lack of FDA premarket review apply to the smaller vial too.
- For the prescriber conversation: this version is compounded, usually below the labeled start, and unstudied as a combination. Weigh those facts before comparing it with an approved pen.
From Our Founders
"I read Lilly's March 12, 2026 letter next to SURMOUNT-1. The impurity data they published were on B12 mixes; glycine is listed there as another untested add-in, not as a proven upgrade, and the 15–21% figures are for approved 5–15 mg pens. Talk to your provider about which vial you would actually use." — Ariel Bowerman, BSN, R.N.
Frequently Asked Questions
What are the benefits and risks of tirzepatide injectable with glycine? Benefits are inferred from approved tirzepatide, not proven for this mix. Risks include usual GI effects plus an unstudied combination, and with microdose vials an unstudied dose as well.
Does any FDA approval cover tirzepatide with glycine? No.
Can glycine make tirzepatide more effective? That has not been established.
What dose is used, and what is a "microdose"? Approved products start at 2.5 mg weekly. Compounded strengths vary, and "microdose" usually means below that labeled start; it is not an FDA-defined dose. This page does not give a home dose.
Should glycine be given separately instead? A clinician can address glycine as its own supplement. Same-vial mixing is the unreviewed step.
Why did Eli Lilly mention glycine? The March 12, 2026 letter listed glycine among untested additives used with compounded tirzepatide.
What side effects were most frequent in SURMOUNT-1? Nausea, in about 25–33% on 5–15 mg approved tirzepatide, followed by diarrhea, constipation, and vomiting. Those are not rates for this compounded mix.
Who is not a candidate for this mix? People with MTC/MEN2, a relevant allergy, or a research-only product. A clinician decides the rest.
Is compounded tirzepatide with glycine interchangeable with Zepbound? No.
Bottom Line
FDA-approved tirzepatide at 5–15 mg has established trial data. Compounded tirzepatide with glycine is not FDA-approved at any strength, and the microdose version is usually below the labeled start. Lilly named glycine as an untested add-in in March 2026. Do not treat glycine as a weight-loss booster.
So what? Ask whether you would get an approved pen or a compounded glycine vial — and whether glycine, if used at all, can be given separately.
Have questions about medical weight management? Talk with a licensed healthcare provider. To learn more or request a consultation, visit Dominia Health.
Sources:
- Jastreboff AM, et al. SURMOUNT-1. NEJM 2022. https://www.nejm.org/doi/full/10.1056/NEJMoa2206038
- Lilly SURMOUNT-1 AE table, June 4, 2022. https://investor.lilly.com/news-releases/news-release-details/lillys-surmount-1-results-published-new-england-journal-medicine
- Lilly open letter, March 12, 2026. https://investor.lilly.com/news-releases/news-release-details/open-letter-eli-lilly-and-company-warning-potential-patient
- Reuters, March 12, 2026. https://www.reuters.com/business/healthcare-pharmaceuticals/lilly-finds-impurity-compounded-version-its-weight-loss-drug-warns-health-risks-2026-03-12/
- FDA unapproved GLP-1 page. https://www.fda.gov/drugs/drug-alerts-and-statements/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
Written by: Dominia Health education
Medically reviewed by: Ariel Bowerman, BSN, R.N.
Published: September 10, 2026 · Updated: October 10, 2026
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