Acetylcysteine is the generic name (oral) [a-SEE-il-SIS-teen]
Names of brands: NAC, N-A-C Sustain

What’s the NAC?

NAC is used to help stop or lessen the damage that taking a lot of acetaminophen does to the liver (Tylenol).

There are other brands and types of acetylcysteine, and some of them can be bought without a prescription. Not all forms of NAC can be used as an antidote to acetaminophen. Do not try to treat an overdose of acetaminophen without first talking to a doctor.

NAC can also be used for things that aren’t mentioned in this guide.


In a serious situation, you might not be able to tell people about your health problems. Make sure that any doctor who treats you in the future knows that you have taken this medicine.

Before you take this drug

If you are allergic to NAC, you shouldn’t use it.

If you can, tell your caregivers before you get NAC if you’ve ever had:

  • Stomach ulcer
  • Stomach bleeding, or bleeding in your esophagus (esophageal varices);
  • High blood pressure or a low-salt diet;
  • Congestive heart failure; or
  • Kidney disease.

If you are pregnant or nursing, you should talk to a doctor before taking NAC.

You might not be able to tell people who are helping you if you are pregnant or breastfeeding in an emergency. Make sure that any doctor who is taking care of you or your baby knows that you have been taking this medicine.

What do I do with NAC?

Follow the directions on the label or what your doctor tells you to do.
If you don’t understand how to take NAC at home, don’t do it.
If you are in a hospital emergency room, do the following: Before you take NAC, your doctors or nurses will check your blood to see how much acetaminophen is in your body. This test works best when done between 4 and 8 hours after an overdose of acetaminophen. If you don’t know when or how much acetaminophen you took last, you will probably get your first dose of acetylcysteine right away.

Your doctor will figure out how long you should take NAC. Take this medicine until your doctor tells you to stop.

If you throw up after taking NAC within an hour, you may need to take another dose.

Keep at room temperature and away from heat and moisture.

What will happen if I don’t take a dose?

Take the medicine as soon as you can, but skip the dose you missed if your next dose is almost due. Take only one dose at a time.

What happens if I overdose?

Get help from a doctor right away or call 1-800-222-1222 to reach the Poison Help line.

What should I stay away from while I’m on NAC?

Follow your doctor’s advice about what you can and cannot eat, drink, or do.

NAC side effects

If you have hives, trouble breathing, or swelling in your face, lips, tongue, or throat, you may be having an allergic reaction.

NAC could have some very bad side effects. Call your doctor right away if you have:

  • Severe or ongoing vomiting;
  • Coughing up blood or vomit that looks like coffee grounds; or
  • Signs that the medicine may not be working, such as upper stomach pain, loss of appetite, dark urine, clay-colored stools, or jaundice (yellowing of the skin or eyes).

Some common side effects of NAC are feeling sick,

  • Throwing up, or having an upset stomach,
  • Getting a rash, or
  • Getting a fever.

This isn’t a full list of all possible side effects, and there may be others. You should talk to your doctor about any side effects. You can call 1-800-FDA-1088 to tell the FDA about side effects.

How will other medicines affect NAC?

Other drugs, like prescription and over-the-counter drugs, vitamins, and herbal products, may have an effect on NAC. Tell your doctor about all the medicines you are taking now, as well as any you start or stop taking.

Where can I find out more about this?

Remember to keep this and all other medicines out of reach of children, to never give your medicines to other people, and to only use this medicine for what it was prescribed for.

About the NAC (acetylcysteine)

  • See what’s going on
  • Reviews (6)
  • Side effects
  • Information about dosage
  • When pregnant or breastfeeding
  • En español

Patient resources
Different brands

Mucomyst, N-A-C Sustain, Acetadote, Acys-5 and Cetylev

Tools for professionals

  • Information for Doctors

    Related treatment guides

    • Supplementing Your Diet

    For more details

    Talk to your doctor or other healthcare provider to make sure that the information on this page applies to your situation.

    Disclaimer for Medical

    Use Copyright 1996–2023 Cerner Multum, Inc. Version: 3.01.

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