Acetylcysteine Uses, Side Effects & Warnings (2024)

Generic name: acetylcysteine (oral) [a-SEET-il-SIS-teen]
Brand names: NAC, N-A-C Sustain
Dosage forms: oral capsule (500 mg; 600 mg), oral tablet (600 mg)
Drug classes: Antidotes, Mucolytics

Medically reviewed by on Dec 25, 2023. Written by Cerner Multum.

What is acetylcysteine?

Acetylcysteine is used to help prevent or lessen liver damage caused by taking large quantities of acetaminophen (Tylenol).

There are other brands and forms of acetylcysteine available, and some can be purchased over the counter. Not all forms of acetylcysteine are effective as an acetaminophen antidote. Do not attempt to treat an acetaminophen overdose without medical advice.

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

Acetylcysteine side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Acetylcysteine may cause serious side effects. Call your doctor at once 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--upper stomach pain, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Common side effects of acetylcysteine may include:

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.

Acetylcysteine side effects (more detail)

Related/similar drugs

ascorbic acid, ambroxol, biotin, multivitamin, Dextrose, niacin, Mucinex DM


In an emergency, you may not be able to tell caregivers about your health conditions. Make sure any doctor caring for you afterward knows you received acetylcysteine.

Before taking this medicine

You should not use acetylcysteine if you are allergic to it.

If possible before you receive acetylcysteine, tell your caregivers if you have ever had:

  • a stomach ulcer;

  • stomach bleeding or bleeding in your esophagus (esophageal varices);

  • high blood pressure, or if you are on a low-salt diet;

  • congestive heart failure; or

  • kidney disease.

Ask a doctor before using this medicine if you are pregnant or breastfeeding.

In an emergency, you may not be able to tell caregivers if you are pregnant or breast feeding. Make sure any doctor caring for your pregnancy or your baby knows you received this medicine.

How should I take acetylcysteine?

Use exactly as directed on the label, or as prescribed by your doctor.

Do not take acetylcysteine at home if you don't understand all instructions.

If you are in an emergency medical setting: Before you take acetylcysteine, your caregivers will perform a blood test to measure the level of acetaminophen in your body. This test is most effective when performed within 4 to 8 hours after an acetaminophen overdose. If you cannot remember when you last took acetaminophen or how much you took, you will most likely be given the first dose of acetylcysteine right away.

Your doctor will determine how long to treat you with acetylcysteine. Do not stop taking acetylcysteine until your doctor tells you to.

If you vomit within 1 hour after taking acetylcysteine, you may need to take another dose.

Store at room temperature away from moisture and heat.

Detailed Acetylcysteine dosage information

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while taking acetylcysteine?

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

What other drugs will affect acetylcysteine?

Other drugs may affect acetylcysteine, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Acetylcysteine drug interactions (more detail)

Popular FAQ

Fluimucil is a brand name for acetylcysteine sachets and tablets which may be used to clear phlegm and liquefy thick and viscous mucus secretions caused by respiratory conditions such as acute bronchitis, chronic bronchitis, cystic fibrosis, pneumonia, pulmonary emphysema, or bronchiectasis. It is a type of mucolytic. Fluimucil is available over the counter (without a prescription) in most countries that have it. Continue reading

NAC (N-acetyl cysteine) is a supplement that may be used to help people replenish glutathione – the most powerful antioxidant in the body. Levels of glutathione rapidly deplete during oxidative stress or after acetaminophen overdosage. NAC may also be used to help improve fertility, brain health, heart health, and long-term respiratory conditions (such as Asthma or COPD) and reduce the risk of developing certain cancers. In medicine, NAC has been used as an antidote to acetaminophen overdose since the 1960s and to treat those with acute liver failure. Continue reading

More about acetylcysteine

  • Check interactions
  • Compare alternatives
  • Reviews (39)
  • Side effects
  • Dosage information
  • During pregnancy
  • Drug class: antidotes
  • Breastfeeding

Patient resources

  • Acetylcysteine inhalation drug information
  • Acetylcysteine (Inhalation) (Advanced Reading)
  • Acetylcysteine (Intravenous) (Advanced Reading)
  • Acetylcysteine (Oral) (Advanced Reading)
  • Acetylcysteine Effervescent Tablets

Other brands

NAC, Mucomyst, N-A-C Sustain, Acys-5, ... +2 more

Professional resources

  • Acetylcysteine, Acetylcysteine Lysine(Local, Systemic) monograph
  • Acetylcysteine Inhalation (FDA)
  • Acetylcysteine Injection (FDA)
  • Acetylcysteine Solution (FDA)

Other brands

Mucomyst, Cetylev, Acetadote

Related treatment guides

  • Expectoration
  • Acetaminophen Overdose
  • Diagnostic Bronchograms
  • Dietary Supplementation

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 circ*mstances.

Medical Disclaimer

Copyright 1996-2024 Cerner Multum, Inc. Version: 3.01.

Acetylcysteine Uses, Side Effects & Warnings (2024)


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