N-acetyl-L-cysteine is soluble in water and alcohol, and practically insoluble in chloroform and ether.It is a white to white with light yellow cast powder, and has a pKa of 9.5 at 30 °C. Dosage forms
Acetylcysteine is available in different dosage forms for different indications:

Solution for inhalation (Assist, Mucomyst, Mucosil) – inhaled for mucolytic therapy
Intravenous injection (Assist, Parvolex, Acetadote) – treatment of paracetamol/acetaminophen overdose
Nebulized as an inhaled vapor, particularly in the treatment of cystic fibrosis and other acute pulmonary conditions
Oral solution – various indications
Effervescent tablets
Ocular solution – for mucolytic therapy
Tablets – sometimes in a sustained release formula sold as a nutritional supplement
CapsulesThe IV injection and inhalation preparations are, in general, prescription only, whereas the oral solution and the effervescent tablets are available over the counter in many countries. Acetylcysteine is available as a health supplement in the United States, typically in capsule form. Society and culture
NAC was first studied as a drug in 1963. Amazon removed NAC for sale in the US in 2021, due to claims by the FDA of it being classified as a drug rather than a supplement. As of 21 April 2022, the FDA released draft guidance on FDAs policy regarding products labeled as dietary supplements that contain N-acetyl-L-cysteine.NAC was studied as a drug and is today used as a medicine. It has also been sold as a dietary supplement within the United States prior to the advent of the Dietary Supplement Health Education Act (DSHEA 1994).
Lungs
Inhaled acetylcysteine has been used for mucolytic ("mucus-dissolving") therapy in addition to other therapies in respiratory conditions with excessive and/or thick mucus production. It is also used post-operatively, as a diagnostic aid, and in tracheotomy care. It may be considered ineffective in cystic fibrosis. A 2013 Cochrane review in cystic fibrosis found no evidence of benefit.Acetylcysteine is used in the treatment of obstructive lung disease as an adjuvant treatment. Kidney and bladder
Evidence for the benefit of acetylcysteine to prevent radiocontrast induced kidney disease is mixed.Acetylcysteine has been used for cyclophosphamide-induced haemorrhagic cystitis, although mesna is generally preferred due to the ability of acetylcysteine to diminish the effectiveness of cyclophosphamide. Psychiatry
Acetylcysteine has been studied for major psychiatric disorders, including bipolar disorder, major depressive disorder, and schizophrenia.Tentative evidence exists for N-acetylcysteine also in the treatment of Alzheimers disease, autism, obsessive-compulsive disorder, specific drug addictions (cocaine), drug-induced neuropathy, trichotillomania, excoriation disorder, and a certain form of epilepsy (progressive myoclonic). Preliminary evidence showed efficacy in anxiety disorder, attention deficit hyperactivity disorder and mild traumatic brain injury although confirmatory studies are required. Tentative evidence also supports use in cannabis use disorder. Bipolar disorder
In bipolar disorder, N-acetylcysteine has been repurposed as an augmentation strategy for depressive episodes in light of the possible role of inflammation in the pathogenesis of mood disorders. Nonetheless, meta-analytic evidence shows that add-on N-acetylcysteine was more effective than placebo only in reducing depression scales scores (low quality evidence), without positive effects on response and remission outcomes, limiting its possible role in clinical practice to date.