- •Site rotation is the single biggest predictor of injection comfort over a year of protocol. Most "injection problems" are rotation problems.
- •SubQ is now first-line for most users, equivalent steady-state levels to IM with smaller peaks and less site reactivity. The exception is high-volume single-shot doses (>0.5 mL) which still favor IM.
- •Reconstitution math is the source of most peptide dose errors. A BAC water mismatch turns a 250 mcg dose into a 1000 mcg dose without anyone noticing until labs come back wrong.
- •Storage rules vary by compound. Reconstituted GLP-1s are stable longer than reconstituted GH peptides. The labels lie about both.
Overview
The technique side of injections looks like a solved problem, until you're on month four and starting to develop scar tissue at the same two abdominal sites you've been using since day one. This page is the cross-cut for the technique, sites, reconstitution, and storage questions that come up across all three protocols.
For full context, the pillar pages cover the protocol-specific dosing decisions:
- TRT pillar, dosing, schedule, and SubQ vs IM
- GLP-1 pillar, choosing a compound and titration
- Peptides pillar, category-specific protocols
For walkthroughs of injection technique with photos and exact angle/needle guidance, see TRT injection guide and peptide guide.
Site rotation, the durable injection skill
How do I rotate injection sites across TRT, GLP-1, and peptide protocols?
Site rotation is the durable injection skill. The standard cross-protocol map:
| Site | Best for | Needle | Volume cap (typical) |
|---|---|---|---|
| Abdominal SubQ (2-inch ring around navel) | TRT, GLP-1, peptides | 27g × 1/2" | 0.5–1.0 mL |
| Anterior thigh SubQ | TRT, GLP-1, peptides | 27g × 1/2" | 0.5 mL |
| Outer hip / love handle SubQ | TRT, GLP-1 | 27g × 1/2" | 0.5 mL |
| Triceps SubQ | Peptides | 30g × 1/2" | 0.3 mL |
| Ventrogluteal IM | TRT high-volume | 23g × 1" | 1.0–2.0 mL |
| Dorsogluteal IM | TRT (older guidance) | 22g × 1.5" | 1.0–3.0 mL |
| Vastus lateralis IM | TRT | 25g × 1" | 1.0–2.0 mL |
| Deltoid IM | TRT (low volume) | 25g × 1" | 1.0 mL max |
The rule that matters: never hit the same exact site twice within a 7-day window, regardless of dose frequency[2]. "The same site" means the same square inch, moving an inch up or left counts as rotation, but the abdominal grid only has so much real estate, which is why most users add at least one off-abdomen site within month two.
Reconstitution math, where peptide dosing actually goes wrong
How do I calculate peptide doses from vial size and BAC water?
Peptide reconstitution is the source of most dose errors. The math:
Dose (units on U-100 syringe) = (target dose mcg / vial size mcg) × BAC water added (mL) × 100
Worked example: 5 mg vial of BPC-157, target 250 mcg per dose, reconstituted with 2 mL BAC water.
- Concentration: 5000 mcg / 2 mL = 2500 mcg/mL
- Per dose: 250 mcg / 2500 mcg/mL = 0.1 mL = 10 units
The error mode: someone uses 1 mL instead of 2 mL of BAC water. Same vial, same target, but now 10 units delivers 500 mcg. Dose math should be re-done from the BAC water added, not assumed from the last vial.
For an interactive calculator that handles every common vial size, see peptide calculator.
Related guides & tools
Tools and guides that go deeper on the technique and math above.
Calculators
- Peptide reconstitution calculator — BAC water, syringe units, and one-tap blends for 200+ compounds (incl. semaglutide, tirzepatide, BPC-157).
- TRT dose calculator — weekly dose to mL and insulin units per injection.
- Half-life visualizer — single-dose and steady-state curves by compound.
- Vial longevity & cost — doses per vial and cost per shot.
Guides
- TRT injection guide — IM vs SubQ, needle gauge, and site rotation.
- Peptide beginner’s guide — reconstitution and first-injection basics.
- Pillar guides: TRT, GLP-1, and peptides.
In the OptiPin app
OptiPin's injection-site rotation map advances automatically across the six SubQ and IM sites as you log doses, so the next-shot site is always one tap away. The reconstitution calculator is built in, pick the vial, enter BAC water added, set target dose, and the syringe-unit number is computed and stored against the active vial. Vial inventory tracks open dates and discard windows per compound (28 days for most GLP-1s, 30 days for most reconstituted GH peptides), with reorder reminders firing before you run out. For users on multiple compounds, the inventory view is the difference between a calm Friday refill and a frantic Sunday-night reconstitution at the wrong concentration.
Sources
Frequently Asked Questions
SubQ or IM for TRT?
SubQ for nearly all new users. Equivalent steady-state levels to IM[1], smaller peak-trough swing (which helps hematocrit and estradiol management), shorter needle, easier rotation. IM still wins for high-volume single-shot doses (>0.5 mL) and for users already on IM who don't want to switch.
How long is reconstituted peptide actually stable?
Refrigerated, most reconstituted GH-class peptides (CJC-1295, ipamorelin, tesamorelin, BPC-157) hold potency for ~30 days. Reconstituted GLP-1s (semaglutide, tirzepatide, retatrutide) hold ~28 days per most compounding pharmacy guidance, though research-chem stability data extends further at refrigerator temperatures. Lyophilized (powder) shelf life is much longer, 12-24 months refrigerated for most.
What needle gauge for what?
27g × 1/2" U-100 insulin syringe is the cross-protocol default for SubQ, TRT, GLP-1, and most peptides. 30g × 1/2" for low-volume peptides. 23-25g × 1" for IM TRT. 22-23g × 1.5" for ventrogluteal or deeper IM in larger users. Any IM injection in the deltoid is capped at 1.0 mL.
Track Your Protocol in OptiPin
Log doses, forecast hormone and compound levels, rotate sites, daily symptom check-ins, and lab tracking, all private and on-device.
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