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Insulin aspart

Brand names: NovoLog, Fiasp

Insulin aspart is a rapid-acting insulin taken at mealtimes to control the rise in blood sugar after eating.

Brand namesNovoLog, Fiasp
Type of medicineRapid-acting (mealtime) 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 starts working within about 15 minutes (Fiasp even faster). It's used with long-acting insulin or in a pump.

What it's used for

  • Type 1 diabetes
  • Type 2 diabetes

How to take it

  • Inject it 5 to 10 minutes before a meal (Fiasp at the start of a meal or within 20 minutes after starting), as your provider says.
  • Rotate injection spots.
  • Never share pens, even with a new needle.

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
  • Redness or lumps where you inject
Call 911Severe low blood sugar: confusion, seizure, or passing out. Use glucagon if you have it, then call 911.
Call your provider todayFrequent low blood sugar or readings that stay high
Call your provider todayMuscle weakness or cramps (low potassium)

Warnings

  • Never inject it without eating soon after.
  • Know the signs of low blood sugar and keep fast sugar with you.

Other medicines, foods, and alcohol

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

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

Pregnancy and breastfeeding

Insulin is used in pregnancy. Work closely with your provider.

Missed doses, overdose, and storage

If you miss a dose

If you forget a mealtime dose, check your blood sugar and follow the plan your provider gave you.

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 pens and vials in the refrigerator (don't freeze). Once opened, follow the label for how long it lasts at room temperature.

Conditions it's used for

Sources

Last updated 2026-11-13.