Skip to content
DosePep
Calculator
Open menu Close menu

DosePep / guides

Guides: Syringes, Vials, and Dose Math

These guides explain the tools and the math behind the dose you were prescribed: mixing a vial, reading the lines on a syringe, needle sizes, injection sites, and mistakes that have been reported.

Last updated

Every guide is for information only and lists its sources. None of them picks a dose, changes your schedule, or points you to a place to buy. To work out the units for your medicine, start with the DosePep calculator and check the strength (mg per mL) printed on your exact vial.

All guides

Short guides in plain language. Each one links to the label or study it came from.

Open the calculator
  1. 01How to mix (reconstitute) a peptide vialWhere to aim the liquid, what bacteriostatic water is, how to work out the strength, and an example of drawing from a vial.
  2. 02How to read an insulin syringeWhat U-100 units mean, which plunger edge is the reference, and why you should read the lines on your own syringe.
  3. 03Insulin syringe sizesCompare 0.3, 0.5 and 1 mL syringes, and the FDA’s warning about syringes that are too big.
  4. 04Needle gauge and lengthWhat the G number and the mm number on a needle package mean, and why pen needles don’t fit syringes.
  5. 05Units vs mL vs mgHow the three numbers relate, and the FDA reports of dosing errors of 5 to 20 times the intended dose.
  6. 06Injection sitesWhere each product’s label says to inject, how to rotate sites, and each label’s missed-dose rules, side by side.
  7. 07Dosing mistakesThe mix-ups the FDA has seen with compounded GLP-1s, when to throw a vial away, and why not to count pen clicks.
  8. 08Retatrutide WatchWhere the retatrutide trials stand: Phase 3 results, side effects, new journal papers and what comes next.

The medicines explained

How these medicines work, how they compare, and what approved, investigational and research-only mean.

  1. 01What is retatrutide?Trial results, how it works, and where FDA approval stands for a medicine still being studied.
  2. 02Retatrutide TRIUMPH-1 resultsWhy NEJM reports 25.0% and Lilly's press release estimated 28.3% if everyone stayed on treatment.
  3. 03Retatrutide side effectsWhat phase 2 and 3 trials reported, by dose and study.
  4. 04Cagrilintide vs. retatrutideHow an amylin analog, CagriSema and a triple agonist differ.
  5. 05Semaglutide vs. tirzepatideHead-to-head trial results, approved uses, dosing and side effects, side by side.
  6. 06Retatrutide vs. tirzepatideTwo receptors against three, and what the separate trials found.
  7. 07Retatrutide vs. semaglutideAn approved GLP-1 medicine next to one that is still in clinical trials.
  8. 08GLP-1 vs. GIP vs. glucagonWhat each hormone does in the body and why some medicines combine them.
  9. 09What half-life means for peptidesWhy weekly peptides last so long, and what that means for dosing and missed doses.
  10. 10Approved vs. investigational vs. research peptidesFour categories, who checks each one, and which can legally be used in people.
  11. 11What are research peptides?What “research use only” means and how it differs from an approved medicine.

Sources

The medical and device facts on this page come from these sources. We accessed them on September 28, 2026.

  1. 01 FDA alerts about dosing errors with compounded semaglutide · U.S. Food and Drug Administration, 07/26/2024. Accessed 2026-09-28.
  2. 02 Technical Data Sheet – Insulin Syringes · embecta, Rev B, 12/2025. Accessed 2026-09-28.
  3. 03 Ozempic (semaglutide) US Prescribing Information · Novo Nordisk, 05/2026. Accessed 2026-09-28.

Medically reviewed by Ashley Alexis, NDLast reviewed How we review