The tirzepatide label's injection sites, rotation rule and timing, and how a dose reads in units on a vial and syringe. Reported from the label.
"Where to inject tirzepatide" has two answers depending on what is in hand. With a pen, the label's answer is the whole story: three sites, rotate each week, press and hold. With a vial, a second question arrives — how far to draw the plunger — and that one is arithmetic. This page reports both from the ZEPBOUND label (read 2026-10-01) and converts the doses to syringe units. It describes what the label says; it gives no instruction.
The general subcutaneous technique that applies to any peptide — needle length, angle, the CDC and nursing references — is on the peptide injection guide. The dose ladder itself is on the tirzepatide dosage page.
The three sites, as the label names them
| Site |
Who injects, per the label |
Exposure, per the label |
| Abdomen |
Patient or another person |
Similar exposure |
| Thigh |
Patient or another person |
Similar exposure |
| Back of the upper arm |
Another person |
Similar exposure |
The arm restriction is practical, not pharmacological: the pen instructions reserve the back of the upper arm for an injection given by another person. The pharmacology section is explicit that exposure is similar at all three. So a page that ranks the sites for tirzepatide — "the stomach absorbs fastest" — is reporting something the label contradicts. The semaglutide labels list the upper arm without that qualifier, as the semaglutide injection sites comparison shows.
The rotation rule is one line in section 2.4 — "Rotate injection sites with each dose" — and the pen instructions spell it out: the same area of the body may be used, with a different injection site in that area each week. Why rotation appears on every injectable label, including the injection-site reaction figures from a daily peptide's trials, is set out in the injection guide.
Timing rules the label does set
- Day: once weekly. The weekly day may change "as long as the time between the two doses is at least 3 days (72 hours)".
- Time of day: none — "at any time of day, with or without meals".
- Missed dose: within 4 days (96 hours) it is taken; after that it is skipped and the regular day resumes.
- Appearance: "clear and colorless to slightly yellow"; the label rules out use with particles or discolouration.
After an injection the label's pharmacology section puts peak concentration at a median of 24 hours (8 to 72), and steady state after four weekly doses. The half-life arithmetic behind those numbers is on the tirzepatide half-life page; splitting a weekly amount into smaller injections, which the label does not describe, is covered on tirzepatide split dosing.
Pen or vial: why a vial adds a reading step
The approved presentations are built so that nobody reads units. Every single-dose pen and vial holds one dose in 0.5 mL; the multi-dose vial and KwikPen hold four 0.6 mL doses. The KwikPen's instructions also tell users not to count clicks; the charts that do are checked against the label on counting clicks on a Mounjaro pen. What a misread syringe line costs in milligrams at each Zepbound vial strength is worked out on the Zepbound vial how-to.
| Label strength |
Presentation |
Concentration |
Volume per dose |
On a U-100 syringe |
| 2.5 mg |
Single-dose |
5 mg/mL |
0.5 mL |
50 units |
| 5 mg |
Single-dose |
10 mg/mL |
0.5 mL |
50 units |
| 10 mg |
Single-dose |
20 mg/mL |
0.5 mL |
50 units |
| 15 mg |
Single-dose |
30 mg/mL |
0.5 mL |
50 units |
| 2.5 mg |
Multi-dose (10 mg/2.4 mL) |
4.17 mg/mL |
0.6 mL |
60 units |
| 15 mg |
Multi-dose (60 mg/2.4 mL) |
25 mg/mL |
0.6 mL |
60 units |
The pattern is the point: on an approved vial the unit count stays fixed and the concentration changes. On a research vial it is the other way round — the concentration is set once by the water added, and the unit count changes with every step of the ladder. For vials the label directs "a syringe appropriate for dose administration (e.g., a 1 mL syringe capable of measuring a 0.5 mL or 0.6 mL dose)" and a new syringe and needle each time.
The label's steps in units, research vials
Units on a U-100 syringe = mg ÷ mg/mL × 100. A 10 mg research vial with 1 mL of water is 10 mg/mL; with 2 mL, 5 mg/mL. The volumes for each vial size are on tirzepatide reconstitution.
| Label step |
5 mg/mL |
10 mg/mL |
20 mg/mL |
| 2.5 mg |
50 units |
25 units |
12.5 units |
| 5 mg |
100 units |
50 units |
25 units |
| 7.5 mg |
150 units |
75 units |
37.5 units |
| 10 mg |
200 units |
100 units |
50 units |
| 12.5 mg |
250 units |
125 units |
62.5 units |
| 15 mg |
300 units |
150 units |
75 units |
Two things follow. At 5 mg/mL everything from 7.5 mg upward is more than one 1 mL syringe, and the Open RN nursing text cited on the injection guide caps a subcutaneous injection at 1 mL for adults. At 20 mg/mL the half-unit steps (12.5, 37.5, 62.5) fall between the marks of most barrels. The milligram-to-units conversion sets out the formula and its tenfold misreadings, and reading an insulin syringe covers the marks; the calculator's tirzepatide setting works any vial.
What is not established
The label describes its own presentations only. No label covers a lyophilised research vial of tirzepatide, its concentration or its handling, and the label's site and exposure statements come from the approved solution. Storage and the general mixing procedure are covered on Medibact's how to store peptides and how to reconstitute peptides pages; the compound itself is in Medibact's Tirzepatide guide. Nothing on this page is an instruction; technique and dose belong with the prescriber.
Sources and dates
Opened 2026-10-01: the ZEPBOUND label via openFDA (Eli Lilly, effective 2026-08-28) — section 2 (dosage and administration, missed dose, administration instructions), section 3 (dosage forms and strengths), section 12.3 (pharmacokinetics) and the single-dose pen Instructions for Use. Units and concentrations are arithmetic by this site. Corrections go to the contact page.
