Inhaltsstoff-Glossar

N-Acetyl Cysteine

What Is N-Acetylcysteine?

N-acetylcysteine is widely known as a cough suppressant and mucus-dissolving agent under the brand name ACC. Acetylcysteine is the abbreviated form of the name N-acetyl-L-cysteine, commonly referred to as NAC. The value of NAC as a dietary supplement is based on the amino acid cysteine it contains.

Cysteine is a building block of many proteins in the body and, through its sulfur group, stabilizes the three-dimensional structure of biological molecules. Cysteine is particularly important as a building block of glutathione. Glutathione is a universal antioxidant and detoxification system found in every cell of the body.

Where Does N-Acetylcysteine Naturally Occur?

Acetylcysteine is a synthetically produced compound derived from the amino acid L-cysteine and does not occur naturally. Cysteine itself accounts for approximately 2.5% of the protein content in natural dietary proteins. Only the L-form occurs in proteins, whereas the enantiomer D-cysteine does not. Therefore, all subsequent references to cysteine refer exclusively to the L-form.

When acetylcysteine is taken orally, the liver removes the acetyl group, leaving the amino acid cysteine. Cysteine is a proteinogenic, non-essential amino acid that the body uses to synthesize its own proteins.

A unique feature of cysteine is its sulfur content. Only two amino acids—methionine and cysteine—contain a sulfur atom in their side chain. This enables cysteine to form so-called disulfide bridges. As the name suggests, two sulfur atoms (sulfides) from two molecules join to form a strong chemical bond. Disulfide bridges are among the strongest chemical bonds in biology, making cysteine essential for the structural stability of numerous proteins and enzymes.

What Is the Primary Function of N-Acetylcysteine in the Body?

By taking acetylcysteine, the body gains access to cysteine. Cysteine is an essential building block of glutathione, which also consists of glutamic acid and glycine. Every cell in the human body contains glutathione, which acts as a buffer against oxidative stress.

When oxidative stress caused by reactive oxygen species (ROS) becomes excessive, glutathione neutralizes these molecules by becoming oxidized itself. In doing so, it protects other cellular structures—such as mitochondrial membranes—from oxidative damage. The body subsequently regenerates glutathione through energy-dependent processes, restoring its protective function.

The sulfur group of acetylcysteine—or more precisely of cysteine—plays a decisive role in glutathione's biological activity. Through this sulfur group, glutathione supports the body's detoxification processes. Chemically, the sulfur group is highly reactive, enabling it to attack, bind, and open other compounds and molecules.

Glutathione utilizes this property of its cysteine component to neutralize toxic substances within the body. It binds toxins via the sulfur group, thereby reducing the toxicity of substances such as heavy metals, pesticides, and environmental pollutants. At the same time, this process increases their water solubility, allowing the body to eliminate these toxins more efficiently through the kidneys and urine.

What Are the Benefits of N-Acetylcysteine Supplementation?

Physicians use the detoxifying properties of acetylcysteine and glutathione to treat acetaminophen (paracetamol) poisoning. During the breakdown of acetaminophen by cytochrome P450 enzymes in the liver, a toxic metabolite is produced that damages liver cells. This becomes particularly dangerous when recommended daily doses are exceeded and the body's glutathione stores become depleted. Glutathione binds this toxic acetaminophen metabolite and facilitates its elimination through the urine.

When taken orally, acetylcysteine is intended to dissolve thick mucus and relieve coughing. The mucus produced in the bronchi consists largely of polysaccharides that are held together by disulfide bonds. Because acetylcysteine contains a sulfur group through its cysteine component, it can break these existing disulfide bonds. In this way, acetylcysteine is believed to liquefy mucus and promote expectoration. However, scientific evidence supporting this mechanism remains inconclusive. An alternative explanation for its beneficial effects on coughing is its anti-inflammatory activity. Through its sulfur group, acetylcysteine can bind free radicals that would otherwise cause oxidative damage and activate pro-inflammatory transcription factors.

Longevity researchers assume that mitochondrial dysfunction and excessive oxidative stress within cells contribute to premature aging. These factors increase the risk of chronic diseases such as cancer, type 2 diabetes, and atherosclerosis. Glutathione helps maintain the natural balance of reactive oxygen species (ROS) within cells. It contributes to preserving mitochondrial function and reducing the risk of ROS-related diseases.

The bioavailability of conventionally administered oral glutathione is relatively low. Oral acetylcysteine therefore provides an effective strategy for increasing the body's own glutathione stores by supplying its essential precursor, cysteine. Particularly popular—and supported by several randomized clinical trials—is the combination of NAC with glycine, another important building block of glutathione.

When taken orally, acetylcysteine is considered non-toxic. The therapeutic dosage ranges from 0.4 g to 0.6 g per day. According to the European Food Safety Authority (EFSA), exceeding this dosage may cause gastrointestinal discomfort in sensitive individuals. In the past, intravenous administration of acetylcysteine has occasionally resulted in overdosing and serious adverse reactions.