Hordenine is a natural Phenethylamine compound that occurs in a number of different plants, but especially barley grass. It is structurally similar to the amino acid Tyramine. It antagonized D2-mediated beta-arrestin recruitment indicating functional selectivity. Hordenine inhibited melanogenesis by suppressing cAMP production, which is involved in the expression of melanogenesis-related proteins. Hordenine may be an effective inhibitor of hyperpigmentation. Hordenine is an indirectly acting adrenergic drug. It liberates norepinephrine from stores. In isolated organs and those structures with reduced epinephrine contents, the hordenine-effect is only very poor. Experiments in intact animals (rats, dogs) show that hordenine has a positive inotropic effect upon the heart, increases systolic and diastolic blood pressure, peripheral blood flow volume, inhibits gut movements but has no effect upon the psychomotorical behavior of mice. Hordenine is considered to be generally very safe and well-tolerated in healthy adults. Hordenine is a nootropic compound that works equally well for cognitive enhancement and athletic performance.

4-Piperidinol, 1-phenethyl-4-phenyl acetate (PEPAP) is a synthetic opioid discovered by Janssen in 1960. PEPAP is an analog of meperidine, it is abused and illegally sold on streets as a "synthetic heroin".

Methyl aminolevulinate is a prodrug that is metabolised to Protoporphyrin IX (a photosensitizer) used in photodynamic therapy. Photosensitization following application of methyl aminolevulinate cream occurs through the metabolic conversion of methyl aminolevulinate (prodrug) to photoactive porphyrins (PAP), which accumulates in the skin lesions to which the cream has been applied. When exposed to light of appropriate wavelength and energy, the accumulated photoactive porphyrins produce a photodynamic reaction, resulting in a cytotoxic process dependent upon the simultaneous presence of oxygen. The absorption of light results in an excited state of porphyrin molecules, and subsequent spin transfer from photoactive porphyrins to molecular oxygen generates singlet oxygen, which can further react to form superoxide and hydroxyl radicals. Methyl aminolevulinate is used for topical use, in combination with 570 to 670 nm wavelength red light illumination, in the treatment of non-hyperkeratotic actinic keratoses of the face and scalp in immunocompetent patients when used in conjunction with lesion preparation (debridement using a sharp dermal curette).

Methylparaben (E number E218) is preservative in the food, cosmetic, and pharmaceutical industries. It is completely absorbed through the skin or after ingestion and and it is hydrolyzed to para-hydroxybenzoic acid, and metabolites are rapidly excreted in the urine. Methylparaben is on the FDA generally regarded as safe list.