Generic name: insulin aspart [ IN-su-lin-AS-part ]
Brand names: Fiasp, NovoLOG, NovoLOG FlexPen, NovoLOG PenFill
Drug class: Insulin

Medically reviewed by Drugs.com on Mar 27, 2025. Written by Cerner Multum.

What is NovoLog FlexPen?

Insulin is a hormone that works by lowering levels of glucose (sugar) in the blood. NovoLog FlexPen is a fast-acting insulin that starts to work about 15 minutes after injection, peaks in about 1 hour, and keeps working for 2 to 4 hours.

NovoLog FlexPen is used to improve blood sugar control in adults and children with diabetes mellitus. NovoLog FlexPen is sometimes used together with a long-acting or intermediate-acting insulin.

NovoLog FlexPen may also be used for purposes not listed in this medication guide.

NovoLog FlexPen side effects

Get emergency medical help if you have signs of insulin allergy: redness or swelling where an injection was given, itchy skin rash over the entire body, trouble breathing, fast heartbeats, feeling like you might pass out, or swelling in your tongue or throat.

NovoLog FlexPen may cause serious side effects. Call your doctor at once if you have:

• heart problems--swelling, rapid weight gain, feeling short of breath; or

• low potassium--leg cramps, constipation, irregular heartbeats, fluttering in your chest, increased thirst or urination, numbness or tingling, muscle weakness or limp feeling.

Common side effects of NovoLog FlexPen may include:

• low blood sugar;

• weight gain;

• low potassium;

• swelling in your hands and feet;

• skin rash, itching, redness, or swelling; or

• thickening or hollowing of the skin where you injected the medicine.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Related/similar drugs

Warnings

Never share an injection pen, cartridge, or syringe with another person, even if the needle has been changed.

Before taking this medicine

You should not use NovoLog FlexPen if you are allergic to it, or if you are having an episode of hypoglycemia (low blood sugar).

NovoLog FlexPen is not approved for use by anyone younger than 2 years old, and should not be used to treat type 2 diabetes in a child of any age. Fiasp is for use only in adults.

Tell your doctor if you have ever had:

• liver or kidney disease; or

• low levels of potassium in your blood (hypokalemia).

Tell your doctor if you also take pioglitazone or rosiglitazone (sometimes contained in combinations with glimepiride or metformin). Taking certain oral diabetes medicines while you are using insulin may increase your risk of serious heart problems.

Tell your doctor if you are pregnant or breastfeeding.

Follow your doctor's instructions about using insulin if you are pregnant or you become pregnant. Controlling diabetes is very important during pregnancy, and having high blood sugar may cause complications in both the mother and the baby.

How should I use NovoLog FlexPen?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

NovoLog FlexPen is injected under the skin, or as an infusion into a vein. A healthcare provider will give your first dose and may teach you how to properly use the medication by yourself.

Your healthcare provider will show you where on your body to inject NovoLog FlexPen. Use a different place each time you give an injection. Do not inject into the same place two times in a row.

Do not inject NovoLog FlexPen into skin that is damaged, tender, bruised, pitted, thickened, scaly, or has a scar or hard lump.

After using Novolog, you should eat a meal within 5 to 10 minutes. Fiasp should be given at the start of a meal or within 20 minutes after starting a meal.

Read and carefully follow any Instructions for Use provided with your medicine. Ask your doctor or pharmacist if you do not understand these instructions.

Prepare an injection only when you are ready to give it. This medicine should be clear and colorless. Do not use the medicine if it has changed colors or has particles in it. Call your pharmacist for new medicine.

If you use an injection pen, use only the pen provided with your medicine. If you use this medicine with an insulin pump, do not mix or dilute NovoLog FlexPen with any other insulin. Change the medicine in the reservoir at least every 6 days.

Never share an injection pen, cartridge, or syringe with another person, even if the needle has been changed. Sharing these devices can allow infections or disease to pass from one person to another.

You may have low blood sugar (hypoglycemia) and feel very hungry, dizzy, irritable, confused, anxious, or shaky. To quickly treat hypoglycemia, eat or drink a fast-acting source of sugar (fruit juice, hard candy, crackers, raisins, or non-diet soda).

Your doctor may prescribe a glucagon injection kit in case you have severe hypoglycemia. Be sure your family or close friends know how to give you this injection in an emergency.

Also watch for signs of high blood sugar (hyperglycemia) such as increased thirst or urination.

Blood sugar levels can be affected by stress, illness, surgery, exercise, alcohol use, or skipping meals. Ask your doctor before changing your dose or medication schedule.

NovoLog FlexPen is only part of a treatment program that may also include diet, exercise, weight control, blood sugar testing, and special medical care. Follow your doctor's instructions very closely.

Keep this medicine in its original container protected from heat and light. Do not draw insulin from a vial into a syringe until you are ready to give an injection. Do not freeze insulin or store it near the cooling element in a refrigerator. Throw away any insulin that has been frozen.

Storing unopened (not in use) NovoLog FlexPen:

• Refrigerate and use until expiration date; or

• Store at room temperature and use within 28 days.

Storing opened (in use) NovoLog FlexPen:

• Store the vial in a refrigerator or at room temperature and use within 28 days.

• Store the cartridge or injection pen at room temperature (do not refrigerate) and use within 28 days. Do not store the injection pen with a needle attached.

Use a needle and syringe only once and then place them in a puncture-proof "sharps" container. Follow state or local laws about how to dispose of this container. Keep it out of the reach of children and pets.

In case of emergency, wear or carry medical identification to let others know you have diabetes.

What happens if I miss a dose?

Since NovoLog FlexPen is used before meals, you may not be on a timed dosing schedule. Whenever you use NovoLog FlexPen, be sure to eat a meal within 5 to 10 minutes. Do not use extra this medicine to make up a missed dose.

Keep insulin on hand at all times. Get your prescription refilled before you run out of medicine completely.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. Insulin overdose can cause life-threatening hypoglycemia. Symptoms include drowsiness, confusion, blurred vision, numbness or tingling in your mouth, trouble speaking, muscle weakness, clumsy or jerky movements, seizure (convulsions), or loss of consciousness.

What should I avoid while using NovoLog FlexPen?

Insulin can cause low blood sugar. Avoid driving or operating machinery until you know how NovoLog FlexPen will affect you.

Avoid medication errors by always checking the medicine label before injecting your insulin.

Avoid drinking alcohol or using medicines that contain alcohol. Alcohol can cause low blood sugar and may interfere with your diabetes treatment.

What other drugs will affect NovoLog FlexPen?

Insulin may not work as well when you use other medicines at the same time. Some drugs can also cause you to have fewer symptoms of hypoglycemia, making it harder to tell when your blood sugar is low. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all medicines you start or stop using.

Novolog flexpen Biosimilars

Biosimilar and interchangeable products are biological products that are highly similar to and have no clinically meaningful differences from the reference product.

Reference products

These are biological products that have already been approved by the FDA, against which biosimilar products are compared. There is 1 for NovoLog FlexPen.

biosimilar products

Biosimilar products can only be dispensed in place of the reference product if the healthcare provider specifically prescribes the biosimilar product by name.

Pharmacy laws for biosimilar prescribing may vary by state

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Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Medical Disclaimer

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