Insulins

Regular (short-acting) insulin: Humulin R, Novolin R

human insulin (regular) · Short-acting insulin · Eli Lilly; Novo Nordisk

✓Last reviewed · Written by Dr. George Grunberger · Medical review: pending — clinician review in progress · How we review

In short

Regular insulin (human insulin (regular)) is a short-acting insulin made by Eli Lilly; Novo Nordisk, used for blood sugar control in diabetes. Schedule: before meals. It is prescription-only in the US and Canada.

FormVials, pens
How oftenBefore meals
United StatesFDA-approved. U-100 is sold over the counter at many US pharmacies; Humulin R U-500 requires a prescription.
CanadaAvailable in Canada.
PrescriptionRequired

What it is used for

  • Blood sugar control in diabetes

Regular insulin dosage

Per the official label. Your prescriber sets your dose — never change it on your own.

Regular insulin label dosing schedule
1DoseIndividualized in units
2TimingAbout 30 minutes before a meal

How to take it

Under the skin.

Storage

Unopened: refrigerate. In use: per product labeling (often 31–42 days).

How long it works compared with other insulins

How long each insulin type worksApproximate duration of action: rapid-acting about 4 hours, regular about 6 hours, NPH 12 to 18 hours with a peak at 4 to 12 hours, glargine about 24 hours, degludec up to 42 hours, icodec about one week.0 h12 h24 h36 h48 hRapid-acting (lispro, aspart, glulisine)Short-acting (regular)Intermediate (NPH)Long-acting (glargine)Ultra-long (degludec)Once-weekly (icodec)≈ 1 week →
Typical time-action profiles from product labels (darker band = peak). Your response can differ — follow your own plan.

Side effects

Common

  • Low blood sugar (hypoglycemia)
  • Injection-site reactions
  • Weight gain
  • Lipodystrophy or skin thickening at repeated injection sites

Serious — get medical help

  • Severe hypoglycemia (confusion, seizures, loss of consciousness)
  • Low potassium (hypokalemia)
  • Fluid retention and heart failure when combined with thiazolidinediones
  • Serious allergic reactions

Who should not use it

  • During an episode of low blood sugar
  • Never share pens or needles, even if the needle is changed
  • Do not switch insulin type, brand or concentration without your prescriber

Cost

Among the lowest-cost insulins in the US.

GLP-1 cost without insurance →

How to buy Regular insulin legally

  1. Get a prescription from your doctor or a licensed telehealth provider.
  2. Fill it at a licensed pharmacy, or through the manufacturer's self-pay pharmacy.
  3. Verify any online pharmacy first (US: safe.pharmacy; Canada: your provincial pharmacy college register).

Buying legally in the USA → Buying legally in Canada →

Frequently asked questions

Is U-500 the same as U-100?

No. U-500 is five times more concentrated and must only be used with its dedicated pen or U-500 syringe.

Also searched as: Humulin R, Novolin R, regular insulin, short-acting insulin, U-500 insulin, over the counter insulin

Sources

Checked against these primary sources on .

InsulinsNPH (intermediate-acting) insulin: Humulin N, Novolin Nisophane human insulin · Once or twice dailyInsulinsPremixed insulins: Humalog Mix, NovoLog Mix, Humulin/Novolin 70/30premixed insulin · Usually twice daily with meals
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