The injection is the part of a GLP-1 that people picture, and it is the part least written about accurately. Coverage tends to collapse seven products into one routine — a weekly shot in the stomach — when the labels differ on who may use which site, on why sites are rotated, on how long a pen survives outside a refrigerator, and even on whether a given brand comes as an injection at all any more.
This page is the anatomy and the hardware, read from the labels. It is not instruction: nothing here describes how to perform an injection, and the technique for any particular device belongs to that device's Instructions for Use and to the prescriber who supplied it, as our editorial standards set out. The comparison between injecting and swallowing the same molecule is on GLP-1 pill vs injection.
Subcutaneous, and what that settles
Every GLP-1 in this set is given subcutaneously — into the fat layer beneath the skin, not into muscle and not into a vein. That single word explains most of the rest. It is why the three named sites are the three places most bodies carry an accessible fat layer, why absorption is slow enough for a weekly product to make sense, and why the needle is short.
It also settles a question people ask in the other direction: these are not intravenous drugs, no drip is involved, and the depth is measured in millimetres.
The three sites, and the one that comes with a condition
| Product (molecule) | Sites the label names | Upper arm |
|---|---|---|
| Wegovy (semaglutide) | abdomen, thigh, upper arm | no condition stated |
| Ozempic injection (semaglutide) | abdomen, thigh, upper arm | no condition stated |
| Mounjaro (tirzepatide) | abdomen, thigh, back of upper arm | another person injects |
| Zepbound (tirzepatide) | abdomen, thigh, back of upper arm | another person injects |
| Trulicity (dulaglutide) | abdomen, thigh, upper arm | no condition stated |
| Byetta (exenatide) | abdomen, thigh, upper arm | no condition stated |
| Saxenda (liraglutide) | abdomen, thigh, upper arm | no condition stated |
The difference in the right-hand column is a real one and it is easy to miss, because both wordings list three sites and only one of them constrains the third. Lilly's two tirzepatide labels read: inject subcutaneously in the abdomen, thigh, or have another person inject in the back of the upper arm. Novo Nordisk's labels and Lilly's own Trulicity label simply list the upper arm among the three.
The labels do not explain the difference, and this page will not invent a reason for it. What can be said is that it is specific to the two tirzepatide products rather than to a manufacturer, since Trulicity is a Lilly product without the condition.
The site does not change the dose
This is the part that removes most of the anxiety around choosing. The Zepbound label states plainly that similar exposure was achieved with administration in the abdomen, the thigh or the upper arm, and puts tirzepatide's mean absolute bioavailability at 80% by this route. The Wegovy label makes the same point from the other direction: the time of day and the injection site can be changed without the need for a dosage modification.
For comparison, the semaglutide labels put subcutaneous bioavailability at 89%. Both figures sit in a different universe from the 0.4% to 1% the same molecule achieves as a tablet — the arithmetic behind that gap is on the route comparison.
Rotation, and the one label that says why
Six of the seven labels instruct rotation in some form. The wordings are not identical:
- Mounjaro, Zepbound, Trulicity: rotate injection sites with each dose.
- Ozempic: use a different injection site each week when injecting in the same body region.
- Byetta: change sites within the chosen area for each dose, and do not use the same site each time.
- Saxenda: rotate within the same region in order to reduce the risk of cutaneous amyloidosis.
- Wegovy: no rotation instruction of its own; it states the site may be changed freely.
Only Saxenda attaches a reason, and the reason is a specific, named reaction. Cutaneous amyloidosis is a deposit of protein material in the skin that can build up where injections are repeatedly given in the same spot, and where it forms, absorption from that patch of skin can be affected. Saxenda lists it under skin and subcutaneous tissue disorders. Mounjaro and Zepbound list it too. Wegovy, Ozempic, Trulicity and Byetta do not mention it anywhere.
That is a genuine inconsistency in the class's documentation rather than a finding about the drugs: the same molecule family, the same route, the same repeated-site behaviour, and one label in three tells the reader what the rotation instruction is protecting against.
The device zoo, and why the carton matters more than the brand
The seven products are supplied in at least five different physical formats, and the format — not the molecule — determines several of the rules.
| Presentation | Products |
|---|---|
| Single-dose pen (one dose, then discarded) | Wegovy, Mounjaro, Zepbound, Trulicity |
| Single-dose prefilled syringe | Wegovy, Ozempic |
| Multi-dose pen, several doses per pen | Ozempic (with NovoFine Plus needles), Wegovy FlexTouch (4 doses), Zepbound KwikPen, Mounjaro KwikPen |
| Single-dose vial | Mounjaro, Zepbound |
| Multi-dose vial | Zepbound |
The Wegovy label acknowledges the problem this creates. It instructs prescribers to tell patients and caregivers which presentation they will receive, to ensure training appropriate to that specific presentation, and — if the prescribed presentation changes — to retrain and redirect them to the new Instructions for Use. A brand name no longer identifies a device, in the same way it no longer identifies a dosage form.
One accessibility limitation is stated outright and is rarely reported: the Wegovy label says FlexTouch is not recommended for self-administration by those who are visually impaired. Its FlexTouch-specific warning was added in 06/2026.
Never shared, with one apparent exception
Six of the seven labels carry a never-share warning — a pen must never be shared between patients even if the needle is changed, because pen-sharing risks transmitting blood-borne pathogens.
Trulicity is the exception, and the exception is about hardware rather than safety. Trulicity is supplied only as a single-dose pen, discarded after one use, so there is no multi-use device for the warning to attach to. The absence of the sentence is not a statement that sharing would be safe.
Storage: a four-fold spread, and two answers inside one brand
Every product in the set is refrigerated at 2°C to 8°C (36°F to 46°F). What differs is how long it may be out.
| Product and presentation | Out-of-fridge allowance | Temperature |
|---|---|---|
| Trulicity single-dose pen | 14 days | up to 30°C (86°F) |
| Mounjaro pen or vial | 21 days | up to 30°C |
| Zepbound pen or vial | 21 days | up to 30°C |
| Wegovy single-dose pen or syringe | 28 days, before cap removal | 8°C to 30°C |
| Ozempic prefilled syringe | 28 days | 8°C to 30°C |
| Ozempic multi-dose pen | 56 days after first use | 15°C to 30°C |
| Wegovy FlexTouch pen | 56 days after first use | 15°C to 30°C |
| Wegovy tablets | not refrigerated at all | 20°C to 25°C |
Two observations follow from that table, and neither is available to someone who knows only the brand.
The allowance runs from 14 days to 56, a four-fold spread across products doing the same job. And a single brand carries two different answers: Wegovy's single-dose pen gets 28 days, its FlexTouch pen gets 56. Ozempic's syringe gets 28, its multi-dose pen 56. The question "how long can it be left out" has no brand-level answer. It has a carton-level answer.
The last row is the one that breaks the frame entirely. Wegovy tablets are stored at room temperature in their original bottle and never see a refrigerator, because they are not an injection at all.
Timing, and the contrast that makes the point
Every injectable here is permitted at any time of day, with or without meals. The weekly products specify the same day each week; Wegovy adds that the day and the time can be changed without a dosage adjustment. Saxenda, the daily injectable, says without regard to the timing of meals.
Set that against the tablets, where absorption happens in the stomach through a narrow window and the surrounding hours determine how much drug gets in. The injection's freedom from timing is not a convenience feature. It is a consequence of bypassing the digestive tract, which is the same fact that produces the bioavailability gap.
What the labels do not settle
- Why the tirzepatide labels restrict the upper arm and the others do not. The documents state the difference without explaining it.
- Why four labels omit cutaneous amyloidosis while three list it. The reaction is a class-plausible consequence of repeated subcutaneous injection, and the labelling is not uniform.
- How often site-related problems actually occur. Adverse reaction listings of this kind come from voluntary postmarketing reports, which cannot give a rate. The counted reactions from the trials are on our side-effects hub.
- Anything about technique. No part of this page describes how an injection is performed, and it should not be read as though it did.
How this page was built
Seven current FDA labels were read in full from DailyMed on 2026-09-18, with each effective date recorded: Wegovy covering injection and tablets (2026-06-18), Ozempic injection (2026-06-01), Mounjaro (2026-08-27), Zepbound (2026-08-28), Trulicity (2026-06-16), Byetta (2025-09-02) and Saxenda (2026-02-25). Injection-site wording, rotation instructions, never-share warnings, presentation lists and section 16 storage text were compared clause by clause across the seven; the tables above record what each document states, and quoted phrases are the labels' own.