n-acetylcysteine, often abbreviated as NAC, is a derivative of the amino acid cysteine.

The name describes the structure of the molecule:

• N-acetyl. This indicates that an acetyl group (CH₃CO-) is attached to the nitrogen atom of the amino group in cysteine.
• Cysteine. This is the amino acid that forms the basis of the molecule. Cysteine is a sulfur-containing amino acid that's used in protein synthesis and as a precursor to other important molecules in the body.

The synthesis process takes place in different steps:

• Preparation of Cysteine. Cysteine, a sulfur-containing amino acid, is the starting material for the synthesis of N-acetylcysteine.
• Acetylation. The amino group of cysteine is then acetylated. This involves reacting cysteine with acetic anhydride or acetyl chloride, which adds an acetyl group (CH₃CO-) to the nitrogen atom of the amino group in cysteine, forming N-acetylcysteine.

It appears in the form of a white powder.

What it is for and where

Medical

• Antioxidant. NAC has antioxidant properties, which means it can help neutralise harmful free radicals in the body. This has led to interest in its potential use in conditions associated with oxidative stress, such as heart disease and cancer, although further research is needed to fully understand its effects in these contexts.
• Mucolytic agent. NAC is commonly used as a mucolytic agent, i.e. it helps to thin and dissolve mucus in the respiratory tract. This makes it easier to cough up mucus and clear the airways, which can be particularly useful for people with chronic respiratory diseases such as chronic obstructive pulmonary disease (COPD) and cystic fibrosis.
• Acetaminophen overdose. NAC is a key treatment for acetaminophen (also known as paracetamol) overdose. In this case, it acts as an antidote to prevent liver damage by replenishing the supply of glutathione, a substance that helps detoxify the harmful metabolite acetaminophen.
• Psychiatric disorders. Some research suggests that NAC may have beneficial effects on the treatment of psychiatric disorders, including bipolar disorder, obsessive-compulsive disorder (OCD) and addictive behaviour, although further research is needed in this area.
• Kidney protection. NAC has been used to protect the kidneys from contrast-induced nephropathy, a type of kidney damage that can occur following certain medical imaging procedures.

Cosmetics

Antioxidant agent. Ingredient that counteracts oxidative stress and prevents cell damage. Free radicals, pathological inflammatory processes, reactive nitrogen species and reactive oxygen species are responsible for the ageing process and many diseases caused by oxidation.

Skin conditioning agent. It is the mainstay of topical skin treatment as it has the function of restoring, increasing or improving skin tolerance to external factors, including melanocyte tolerance. The most important function of the conditioning agent is to prevent skin dehydration, but the subject is rather complex and involves emollients and humectants that can be added in the formulation.

See N-acetylcysteine

• Molecular Formula   C₅H₉NO₃S
• Molecular Weight   163.20 g/mol
• CAS    616-91-1
• UNII    WYQ7N0BPYC
• EC Number 210-498-3