Why do reconstitution pens use 3 mL cartridges?

Precision click-dial pens are engineered to accept standard 3 mL glass cartridges, so reconstitution math and refill schedules are conventionally built around that volume for precision and reproducibility.

What does U-100 mean on a peptide research pen?

U-100 means 100 units fit in every 1 mL of liquid. Units act like ruler tick marks, letting researchers dial to the same position each draw for consistent, repeatable volume delivery.

How do I calculate how many draws a 3 mL cartridge holds?

Divide total cartridge volume by units per draw (3 mL = 300 U-100 units). A peptide calculator planner can automate this and generate a full refill schedule from a single compound or blend entry.

PreppinPeppers › Facts › Lab article

Refilling a GLP-1 Pen: What Reddit Gets Right

Machine-readable facts for this Lab article. The full page is https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit.

TL;DR

Refilling a GLP-1 research pen: a fact-check of Reddit on 3 ml glass cartridges, the U-100 scale (100 units = 1 ml), dialing units and planning refills.

Facts Index

Fact ID	Category	Entity	Attribute	Value	Source
glp1-peptide-pen-cartridge-reddit:title	identity	Refilling a GLP-1 Pen: What Reddit Gets Right	title	Refilling a GLP-1 Pen: What Reddit Gets Right	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:published	identity	Refilling a GLP-1 Pen: What Reddit Gets Right	published	2026-08-15	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:author	identity	Refilling a GLP-1 Pen: What Reddit Gets Right	author	Preppin' Peppers Editorial Team	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:topics	identity	Refilling a GLP-1 Pen: What Reddit Gets Right	topics	community, guides, research	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:summary	content	Refilling a GLP-1 Pen: What Reddit Gets Right	summary	Refilling a GLP-1 research pen: a fact-check of Reddit on 3 ml glass cartridges, the U-100 scale (100 units = 1 ml), dialing units and planning refills.	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:section-1	content	Refilling a GLP-1 Pen: What Reddit Gets Right	section	What it is	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:section-2	content	Refilling a GLP-1 Pen: What Reddit Gets Right	section	Why 3 mL cartridges	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:section-3	content	Refilling a GLP-1 Pen: What Reddit Gets Right	section	Units and dialing	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:section-4	content	Refilling a GLP-1 Pen: What Reddit Gets Right	section	Planning refills	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:section-5	content	Refilling a GLP-1 Pen: What Reddit Gets Right	section	Related reading	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:section-7	content	Refilling a GLP-1 Pen: What Reddit Gets Right	section	What the research community gets wrong about refilling a research pen with 3 mL cartridges	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:product-gansulin-metal-peptide-pen	products	Refilling a GLP-1 Pen: What Reddit Gets Right	references product	Gansulin Pen · Reusable Click-Dial, 3 ml (1-60 Units)	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:source-dailymed-nlm-nih-gov	source	Refilling a GLP-1 Pen: What Reddit Gets Right	cites	NovoLog (insulin aspart) , FDA/DailyMed label confirming 100 units/mL (U-100) and 3 mL PenFill cartridge delivery device - dailymed.nlm.nih.gov	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:source-dailymed-nlm-nih-gov-2	source	Refilling a GLP-1 Pen: What Reddit Gets Right	cites	Humalog (insulin lispro) , FDA/DailyMed label confirming 100 units/mL (U-100) and 3 mL single-patient-use cartridges - dailymed.nlm.nih.gov	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:source-pubmed-ncbi-nlm-nih-gov	source	Refilling a GLP-1 Pen: What Reddit Gets Right	cites	Bohannon, Postgrad Med 1999: Insulin delivery using pen devices. Simple-to-use tools may help young and old alike - pubmed.ncbi.nlm.nih.gov	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:source-pmc-ncbi-nlm-nih-gov	source	Refilling a GLP-1 Pen: What Reddit Gets Right	cites	Jonker et al., Int J Clin Pharmacol Ther 2021: First pre-filled pen device with highly purified human menopausal gonadotropin (HP-hMG, Menopur) in liquid is shown to be bioequivalent to powder for reconstitution - pmc.ncbi.nlm.nih.gov	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)
glp1-peptide-pen-cartridge-reddit:source-pmc-ncbi-nlm-nih-gov-2	source	Refilling a GLP-1 Pen: What Reddit Gets Right	cites	Lingen et al., Endocr Connect 2023: Advantages and disadvantages of connected insulin pens in diabetes management - pmc.ncbi.nlm.nih.gov	Lab article (https://www.preppinpeppers.com/blogs/the-lab/glp1-peptide-pen-cartridge-reddit) (evidence)

FAQ

Why do reconstitution pens use 3 mL cartridges?: Precision click-dial pens are engineered to accept standard 3 mL glass cartridges, so reconstitution math and refill schedules are conventionally built around that volume for precision and reproducibility.
What does U-100 mean on a peptide research pen?: U-100 means 100 units fit in every 1 mL of liquid. Units act like ruler tick marks, letting researchers dial to the same position each draw for consistent, repeatable volume delivery.
How do I calculate how many draws a 3 mL cartridge holds?: Divide total cartridge volume by units per draw (3 mL = 300 U-100 units). A peptide calculator planner can automate this and generate a full refill schedule from a single compound or blend entry.