PharmaceuticalNutrient partitioningHuman insulinShort-acting

Regular Insulin (Humulin R)

Also known as Humulin R · Novolin R · Regular insulin · R

Written by enwyReviewed 5 Aug 20261 sources0 comments

Regular (soluble) human insulin, sold as Humulin R and Novolin R, is unmodified recombinant human insulin with a slower onset (~30 min) and longer action than rapid analogues. It is a historically popular bodybuilding insulin, available over the counter in the US, dosed post-workout for glucose disposal. Hypoglycaemia risk is severe and longer-lasting.

01 Overview

Regular insulin forms zinc hexamers that must dissociate before absorption, giving a slower onset and a 5-8 hour duration. This makes its action window wider and its hypoglycaemia harder to "outlast" than rapid analogues. It has been used clinically for decades and is one of the most studied drugs in medicine.

Because older US regulations allowed OTC purchase, regular insulin became the classic physique-community insulin. Users typically inject post-training with a fixed carbohydrate load. Its longer tail means lows can appear hours later, so monitoring must continue well beyond dosing.

02 Mechanism

Binds the insulin receptor to drive GLUT4-mediated glucose uptake, glycogen and protein synthesis and suppression of lipolysis and gluconeogenesis; hexamer dissociation delays onset and prolongs action versus analogues.

03 Dosing

Tier	Dose	Route	Notes
Beginner (off-label)	2–5 IU	SubQ	With ~10 g carbs per IU; monitor for hours
Common (off-label)	5–10 IU	SubQ	Longer action extends hypoglycaemia window
Diabetic bolus	5–20 IU	SubQ	Individualised; medical use only

04 Effects

Effect	Magnitude	Evidence
Muscle glycogen loadingExtended glucose disposal supports glycogen storage post-training.	Increased fullness and pumps	Clinical
Anabolic / anti-catabolic effectPromotes protein synthesis and reduces breakdown via insulin signalling.		Clinical

05 Side effects

Effect	Severity	Frequency	Evidence	Countermeasures
Fat gain / lipohypertrophyAdipose gain and injection-site fatty lumps.	Mild	Common	Clinical
Prolonged severe hypoglycaemiaBlood glucose crash that can recur or persist across the long action window, causing seizure, coma or death.	Life-threatening	Common in misuse	Clinical

06 Legal status

United Kingdom

POM

as of Jan 2026

United States

Rx-only for analogues; regular insulin sold OTC in many US states

OTC availability varies by state; NPH/regular historically behind-the-counter · as of Jan 2026

07 References

Human insulin pharmacokinetics and clinical useDiabetes Care

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.