According to the World Health Organization (WHO), unwanted effects are classified according to their frequency of development as follows: very often (> 1/10), often (> 1/100, <1/10), infrequently (> 1/1000, <1/100), rarely (> 1/10000, <1/1000) and very rarely (<1/10000); frequency is unknown (the frequency of occurrence of phenomena can not be determined on the basis of available data).
From the immune system
infrequently: hypersensitivity reactions;
very rarely: anaphylactic shock, anaphylactic / anaphylactoid reactions.
From the nervous system
infrequently: headache.
From the side of the cardiovascular system
infrequently: tachycardia;
very rarely: bleeding, lowering blood pressure; frequency unknown: redness.
From the skin and subcutaneous tissues
infrequently: itchy skin, exanthema, urticaria, angioedema, skin rash.
From the respiratory system
rarely: dyspnea, bronchospasm.
From the gastrointestinal tract
infrequently: stomatitis, abdominal pain, nausea, vomiting, diarrhea; rarely: indigestion.
General disorders and disorders at the site of administration
infrequently: fever, tinnitus; frequency unknown: edema of face.
Also, when taking acetyl cysteine, very rarely reported the occurrence of Stevens-Johnson syndrome and Lyell's syndrome (toxic epidermal necrolysis). If skin and mucous membrane changes occur, the doctor should be consulted immediately, and the drug should be discontinued.