Mucomyst Side Effects

Generic Name: acetylcysteine

Note: This page contains information about the side effects of acetylcysteine. Some of the dosage forms included on this document may not apply to the brand name Mucomyst.

Not all side effects for Mucomyst may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to acetylcysteine: inhalation solution

In addition to its needed effects, some unwanted effects may be caused by acetylcysteine (the active ingredient contained in Mucomyst). In the event that any of these side effects do occur, they may 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 of the side effects that can occur with acetylcysteine may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

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 Mucomyst)


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 Mucomyst)

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 Mucomyst) 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 Mucomyst) 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 Mucomyst) was used to prevent perioperative inflammation and ischemia-reperfusion injury during cardiac surgery.

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