NAC Side Effects

Generic Name: acetylcysteine

Note: This page contains side effects data for the generic drug acetylcysteine. It is possible that some of the dosage forms included below may not apply to the brand name NAC.

It is possible that some side effects of NAC may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

Applies to acetylcysteine: inhalation solution

As well as its needed effects, acetylcysteine (the active ingredient contained in NAC) may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking acetylcysteine, check with your doctor or nurse as soon as possible:

Less common
  • Wheezing, tightness in chest, or difficulty in breathing (especially in asthma patients)
  • Skin rash or other irritation

Some acetylcysteine side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

Less common
  • Clammy skin
  • fever
  • increase in amount of mucus in lungs
  • irritation or soreness of mouth, throat, or lungs
  • nausea or vomiting
  • runny nose

For patients using a face mask for inhalation of acetylcysteine: the mask may leave a stickiness on your face. This can be removed with water.

When you use acetylcysteine, you may notice that the medicine has an unpleasant odor at first. However, this smell will go away soon after you use the medicine.

For Healthcare Professionals

Applies to acetylcysteine: compounding powder, inhalation solution, intravenous solution, oral capsule, oral tablet


Gastrointestinal side effects reported after oral administration have included nausea, vomiting, diarrhea, heartburn, dyspepsia, rectal bleeding, and epigastric pain. Stomatitis, hemoptysis, and rhinorrhea have been associated with the use of nebulized acetylcysteine (the active ingredient contained in NAC)


Allergic reactions to intravenous use have occurred. Symptoms have included urticarial rash, pruritus, flushing, a warm feeling of the skin, occasional bronchospasm or hypotension, angioedema, dyspnea, a serum sickness-like reaction, and asthma.


Respiratory side effects, including bronchospasm, wheezing, precipitation of asthma, and respiratory arrest, have been reported after respiratory or intravenous administration. Hemoptysis rarely occurs.

Nervous system

CNS side effects of dizziness, drowsiness, lightheadedness, and asthenia have occurred with oral use. Headache and increased intracranial pressure have been reported rarely.


One case of ST segment depression, chest pain, and T-wave inversion was associated with an anaphylactoid reaction to intravenous acetylcysteine (the active ingredient contained in NAC)

Cardiovascular side effects of tachycardia and hypotension have been reported in patients with hypersensitivity to acetylcysteine.


Skin rashes and pruritus have been reported. Skin reactions are a common presentation of hypersensitivity to intravenous administration.

Rashes seen after intravenous therapy usually consist of transient flushing on the upper trunk, neck and face. Rashes sometimes were urticarial and pruritic.


Local reactions to injectable 20% acetylcysteine (the active ingredient contained in NAC) solution extravasation include severe pain and excoriation.


Fever is a rarely occurring side effect seen after both inhalation and intravenous administration.


Musculoskeletal side effects have rarely included myalgia and arthralgia.


Elevated serum transaminase levels were temporally associated with acetylcysteine (the active ingredient contained in NAC) administration in a patient with cystic fibrosis. At the dose used for acetaminophen toxicity, acetylcysteine does not have hepatotoxic effects.


Hematologic side effects have included increased blood loss and use of blood products when acetylcysteine (the active ingredient contained in NAC) was used to prevent perioperative inflammation and ischemia-reperfusion injury during cardiac surgery.

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