3-Tyrosine, in contrast to the para isomer, is readily racemized. The majority of the load was metabolized to m-hydroxyphenylacetic acid but m-hydroxymandelic acid and 3,4-dihydroxyphenylacetic acid were also detected. Low circulating levels of m-tyrosine in the plasma suggest that most of the load is held due to a first pass effect somewhere in the enterohepatic system and that this portion of the load is not in equilibrium with the plasma m-tyrosine. The metabolism of a m-tyrosine may give further insight into the deficiencies of the phenylalanine hydroxylating system found in the various phenotypes of phenylketonuria. 3-Tyrosine has been used experimentally as a substitute for L-DOPA in the treatment of Parkinsonism. 3-tyrosine mimics the action of Dopa in two experimental animal models. It was also obvious from the experiments with d,l- and l-m-tyrosine that only the l-isomer (3-Tyrosine) is active.

There is no information related to the pharmacological application of DL-thyroxine, but is known, that this is a mixture of two: L (levothyroxine) and D (dextrothyroxine) forms, and it was shown, that levothyroxine possessed greater antioxidative effect, than the DL.

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.

Lysing is an essential basic amino-acid encoded by codone AAA and AAG, and used in the biosynthesis of proteins. The daily requirement for lysine is 38 mg/kg body weight. The most rich source of lysine is fish, beef, chicken. In a clinical study lysine supplements was found to be an effective for reduction of occurrence, severity and healing time for recurrent HSV infection, however Cochrane Review concluded that the evidence is insufficient. Lysine was investigated for improving anxiety, ameliorating angina prectoris. Lysine acetylsalicylate has been used to treat pain and to detoxify the body after heroin use. Lysine clonixinate has been used for its analgesic properties for the treatment of migraine headaches and other painful conditions. However, limited clinical trials exist for these conditions.

Dextrothyroxine is the dextrorotary isomer of the synthetic thyroxine. It is an antihyperlipidemic agent. The mechanism of action is not completely understood, but dextrothyroxine apparently acts in the liver to stimulate formation of low-density lipoprotein (LDL) and, to a much greater extent, to increase catabolism of LDL. This leads to increased excretion of cholesterol and bile acids via the biliary route into the feces, with a resulting reduction in serum cholesterol and LDL. Dextrothyroxine has no significant effect on high-density lipoproteins (HDL). Inherently, it will also bind to thyroid receptors and as it is a prohormone, it will bind as a substrate to iodide peroxidase.

Tyrosine (L-form) is a non-essential amino acid, which is primarily required for the protein synthesis. This amino acid is the precursor of dopamine, norepinephrine, and epinephrine; therefore the lower concentration of tyrosine could be a peripheral marker of the hyperdopaminergic condition hypothesized to explain psychosis. Tyrosine supplements can improve cognition, increase energy, reduce anxiety, reduce depression, reduce levels of pain.