ATC Code R05CB01, S01XA08, V03AB23
Formula C5H9NO3S
Molar Mass (g·mol−1) 163,20
Physical State solid
Melting Point (°C) 106–108
CAS Number 616-91-1
PUB Number 581
Drugbank ID DB06151
Solubility soluble in water and alcohol, practically insoluble in chloroform and ether


Acetylcysteine is a synthetically produced modification (derivative) of the naturally occurring amino acid cysteine. Acetylcysteine is used as an expectorant in respiratory diseases and as an antidote in paracetamoline intoxication. Its effect as an expectorant has not been fully established. It is administered perorally, by inhalation or parenterally. Most forms of acetylcysteine do not require a prescription.



The mucolytic effect is apparently due to the cleavage of disulfide bridges present in mucopolysaccharides (a component of mucus). This makes the mucus thinner and easier to cough up. The effect as a paracetamol antidote comes from the metabolization of acetylcysteine to cysteine. Cysteine is required for the formation of glutathione, which plays a major role in the degradation of paracetamol into non-toxic metabolites.


The bioavailability of acetylcysteine is only 5-10%. This is due to its rapid metabolism to cysteine in the liver. Plasma protein binding is about 83%. The resulting cysteine is absorbed into the body's natural amino acid metabolism and thus metabolized. The half-life is about 5-6 hours.


Acetylcysteine should not be taken together with cough suppressants as this inhibits coughing up. Acetylcysteine inactivates some antibiotics (penicillins, aminoglycosides, tetracycline). For this reason, they should be taken 2 hours apart from each other. Acetylcysteine can increase the effect of glycerol trinitrate, which can possibly lead to life-threatening side effects.


Side effects

Side effects associated with the use of acetycysteine are occasional to rare.

These include:

  • Headache
  • gastrointestinal discomfort
  • Rashes
  • itching
  • Breathing difficulties
  • Hypotension and shock

Toxicological data

LD50 (rat, oral): 5050 mg-kg-1

Markus Falkenstätter

Markus Falkenstätter

Markus Falkenstätter ist Autor zu pharmazeutischen Themen in der Medizin-Redaktion von Medikamio. Er befindet sich im letzten Semester seines Pharmaziestudiums an der Universität Wien und liebt das wissenschaftliche Arbeiten im Bereich der Naturwissenschaften.

Mag. pharm Stefanie Lehenauer

Mag. pharm Stefanie Lehenauer

Stefanie Lehenauer ist seit 2020 freie Autorin bei Medikamio und studierte Pharmazie an der Universität Wien. Sie arbeitet als Apothekerin in Wien und ihre Leidenschaft sind pflanzliche Arzneimittel und deren Wirkung.

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