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Insulin regular

Brand names: Humulin R, Novolin R, Humulin R U-500

Regular insulin is a short-acting insulin taken 30 minutes before meals. Some versions are sold over the counter at lower cost.

Brand namesHumulin R, Novolin R, Humulin R U-500
Type of medicineShort-acting insulin
Prescription?Prescription
ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

It acts more slowly than rapid-acting insulins like lispro or aspart. U-500 is a concentrated form for people needing very high doses.

What it's used for

  • Type 1 and type 2 diabetes
  • Hospital treatment of high blood sugar and DKA (IV)

How to take it

  • Inject 30 minutes before meals, as directed.
  • U-500 must be measured with its own pen or U-500 syringe.
  • Rotate injection spots.

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

  • Low blood sugar
  • Weight gain
  • Injection site reactions
Call 911Severe low blood sugar: confusion, seizure, or passing out. Use glucagon if you have it, then call 911.
Call your provider todayFrequent lows or highs

Warnings

  • Use over-the-counter insulin with a provider's plan.

Other medicines, foods, and alcohol

  • Other diabetes medicines add to low blood sugar risk.
  • Beta blockers can hide signs of low blood sugar.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

Commonly used in pregnancy.

Missed doses, overdose, and storage

If you miss a dose

Check your blood sugar and follow your provider's plan. Don't take a mealtime dose long after eating without guidance.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Keep unopened vials and pens in the refrigerator. Once opened, follow the label for room-temperature use.

Conditions it's used for

Sources

Last updated 2026-11-13.