Milestone bottle

Close-up of Iletin vial-1923. The insulin was all beef, came in varying strengths and was not highly purified.

Regular, neutral, Toronto or Toronto insulin. A term used most often in Canada, Toronto simply another name for R or neutral insulin, no matter who makes it or its origin. Toronto was where Frederick Banting and Charles Best did their work discovering insulin, and terming such insulin Toronto insulin honors their work there.

Human activity profile for r-DNA/GE/GM R (Regular)/Neutral insulin. See links for cat & dog activity.

A short-acting, soluble, non-suspended insulin produced from r-DNA/GE/GM, bovine, or porcine sources. R or neutral insulin is basically zinc insulin crystals dissolved in clear fluid with nothing added to alter its action or speed[1]. From 1921 to the 1930's when PZI was developed, R was the only kind of insulin available.

While both R/neutral and semilente insulins are considered fast-acting, they differ in a few ways. As above, there's no suspension or buffer[2] in R/neutral; it's totally dissolved and soluble, meaning it can safely be used intravenously.

The very small insulin particles in semilente insulin are suspended by zinc[3]. Semilente is cloudy, has an acetate buffer and cannot be used intravenously.

R/Neutral insulin cannot be reliably mixed with Lente or Ultralente insulins[4][5]. Semilente can; the ratio of 3 parts semilente insulin to 7 parts ultralente insulin produces Lente insulin[6].

R/Neutral InsulinsEdit

R/Neutral Insulins

All Short acting
All soluble


Hypurin Bovine Neutral


Hypurin Vet Neutral


Insuvet Neutral


Iletin I R
(No longer produced.)


Hypurin Porcine Neutral
Hypurin Pork Regular


Pork Actrapid


Iletin II R
(No longer produced.)


Humulin R, Humulin S


Insuman Rapid


Actrapid, Novolin R
ReliOn/Novolin R

Further ReadingEdit




  1. US FDA-Humulin R
  2. Auburn University:Insulin Preparations-Regular Insulin
  3. Auburn University: Insulin Preparations-Lente
  4. Intermediate-Acting Insulin Preparations: NPH (Isophane) & Lente Diabetes Care-1980
    Note--in 1980, there was only beef Lente-type insulin--no pork or r-DNA/GE/GMLente insulins
  5. Resource Guide 2005-American Diabetes Association
  6. Auburn University: insulin Preparations-Lente Insulin
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