An essential amino acid.  L-Phenylalanine is also the precursor to l-tyrosine as well as phenethylamine (PEA). It may be included in certain weight loss/bodybuilding supplements for this reason, as both metabolites have mood/cognitive effects.

Phenylalanine is a product of aspartame metabolism.  Various activists insist it’s (partly) responsible for the reputed (and often exaggerated) side effects of the sweetener, since it’s a “neurotoxin” when taken in isolation.  This claim is based on studies of phenylketonuria (PKU), a genetic disorder that affects phenylalanine metabolism.  However, there is no reason to believe that small amounts of phenylalanine, taken in supplemental form, will have any adverse effects on healthy people.

See Acetyl-L-Carnitine.

See Ephedra.

An analog of the amino acid l-cysteine.  NAC is a drug used to a) help dissolve mucus and treat inflammation in respiratory conditions; b) protect against radiocontrast-induced nephropathy; and c) to treat acetaminophen toxicity.  It’s also taken as an oral supplement, as it’s a precursor to glutathione, a potent endogenous antioxidant.  NAC may also have neuroprotective effects in brain injury and exposure to chemotherapeutic drugs.

A non-essential amino acid synthesized in the body from l-serine and l-methionine.  Cysteine is one of the two “sulfur-containing” amino acids found in proteins, and a precursor to the endogenous antioxidant, glutathione.  Cysteine is also an important source of sulfide in human metabolism.

Anecdotally, supplemental cysteine has gained a reputation as a hangover “cure”, as it contributes to the metabolism of acetaldehyde – the toxic ethanol metabolite responsible for those unpleasant, “morning after” symptoms.

Also known as aspartic acid.  L-aspartate is a non-essential amino acid used in the formation of proteins, as well as several other important biochemical reactions, such as the urea cycle and malate-aspartate shuttle.  No specific need for aspartate supplements per se has been identified, although it may be used as a chelating agent for the delivery of certain supplemental minerals (such as zinc or magnesium).

A non-essential amino acid.  Asparagine is the focus of a food processing problem, as it’s a precursor to acrylamide – a potentially carcinogenic compound found in high-heat processed foods such as french fries and potato chips.  Although important to protein synthesis and structure, no role for supplemental asparagine has been identified.

A non-essential amino acid.  L-alanine should not be confused with beta-alanine, a related, but distinct compound.  Alanine is a component of protein and is critical for the glucose-alanine cycle (used by the body to produce glucose from amino acids), but no specific need for supplemental alanine has been identified.

See 5-Methyl-7-Methoxyisoflavone.

The potassium salt of R-alpha-lipoic acid (R-ALA).  The salt form of R-ALA has been found to be more soluble and stable; and hence, more bioavailable than unmodified R-ALA.