Acetylcysteine (also known as N-acetylcysteine or N-acetyl-L-cysteine or NAC) is primarily used as a mucolytic agent and in the management of acetaminophen poisoning. Acetylcysteine likely protects the liver by maintaining or restoring the glutathione levels, or by acting as an alternate substrate for conjugation with, and thus detoxification of, the reactive metabolite. Nacystelyn (NAL), a recently-developed lysine salt of N-acetylcysteine (NAC) is known to have excellent mucolytic capabilities and is used to treat cystic fibrosis (CF) lung disease. NAC as a precursor to the antioxidant glutathione modulates glutamatergic, neurotrophic, and inflammatory pathways. The potential applications of NAC to facilitate recovery after traumatic brain injury, cerebral ischemia, and in treatment of cerebrovascular vasospasm after subarachnoid hemorrhage. Acetylcysteine serves as a prodrug to L-cysteine, which is a precursor to the biologic antioxidant, glutathione, and hence administration of acetylcysteine replenishes glutathione stores. L-cysteine also serves as a precursor to cystine, which in turn serves as a substrate for the cystine-glutamate antiporter on astrocytes hence increasing glutamate release into the extracellular space. Acetylcysteine also possesses some anti-inflammatory effects possibly via inhibiting NF-κB through redox activation of the nuclear factor kappa kinases thereby modulating cytokine synthesis. NAC is associated with reduced levels of inflammatory cytokines and acts as a substrate for glutathione synthesis. These actions are believed to converge upon mechanisms promoting cell survival and growth factor synthesis, leading to increased neurite sprouting.

Cysteine (cysteine hydrochloride is a salt) is a thiol-containing amino acid that is oxidized to form cystine. Cysteine is synthesized from methionine via the trans-sulfuration pathway in the adult, but newborn infants lack the enzyme, cystathionase, necessary to effect this conversion. Therefore, cysteine is generally considered to be an essential amino acid in infants.

Dacisteine is a derivative of a N-acetylcysteine, where a second acetyl group is attached to a sulfur atom. Dacisteine is marketed in France under tradename Mucothiol for the treatment of disorders of bronchial secretion, acute bronchitis and acute episode of chronic bronchopneumopathies. Dacisteine exerts its action on the gel phase of the mucus, presumably by breaking the disulfide bonds of the glycoproteins, and thus promotes the expectoration.

Cystine is the oxidized dimer form of the amino acid cysteine. Cystine serves two biological functions, a site of redox reactions and a mechanical linkage that allows proteins to retain their 3-dimensional structure. It is common in many foods such as eggs, meat, dairy products, and whole grains as well as skin, horns and hair. Human hair and skin contain approximately 10–14% cystine by mass. Cysteine supplements are sometimes marketed as anti-aging products with claims of improved skin elasticity. Cysteine is more easily absorbed by the body than cystine, so most supplements contain cysteine rather than cystine. N-acetyl-cysteine (NAC) is better absorbed than other cysteine or cystine supplements.

Phenylalanine is a biologically essential amino acid that acts as a precursor to tyrosine and the catecholamines (epinephrine, norepinephrine, dopamine, and tyramine), and is a constituent of many central nervous system neuropeptides. Normal dietary levels of phenylalanine are approximately 1-2 grams daily. Phenylalanine appears in two forms which are identical mirror images of each other: L-phenylalanine, a nutritional supplement, and D-phenylalanine, an effective painkiller and antidepressant due to its ability to inhibit the breakdown of enkephalins, the brain’s natural pain killers.

Thiamphenicol aminoacetate is an antibiotic. It is the methyl-sulfonyl analogue of chloramphenicol and has a similar spectrum of activity, but is 2.5 to 5 times as potent. It is used in many countries as a veterinary antibiotic, but is available in China, Morocco and Italy for use in humans. Thiamphenicol aminoacetate is reported as an ingredient of Urfamycin in Ecuador, Indonesia, Italy, Taiwan, Thailand, Turkey, Japan. It is indicated for the treatment of GUT, hepatobiliary, respiratory tract, enteric tract infections, typhoid, paratyphoid fever and salmonellosis, brucellosis.