Oregano (Origanum vulgare L.)
Family – Lamiaceae

Origanum vulgare is an aromatic, wood-based perennial, which grows to 20-90 cm in height. Its leaves are ovate, 10-40 mm long and 5-25 mm wide, and born opposite each other on the stem. The edges of the leaves are smooth or very shallowly toothed, and the leaf tips vary from acute  to obtuse. The inflorescence is many-flowered, with flowers grouped into short dense lateral or terminal spikes. The corolla is white to purplish, 4-8 mm long, and has two lips. Each fruit has four small nutlets (single-seeded units).

Geographic Distribution. Oregano is native to the Mediterranean, Europe (including the British Isles) and south and central Asia, and is cultivated elsewhere.

Habitat. It prefers well-drained soil and can grow in nutritionally poor soil. It can grow in semi-shade (light woodland) or no shade. It prefers dry or moist soil. The plant can tolerates strong winds but not maritime exposure.
 

Chemical composition. Oregano contains essential oil (up 1.2%), which consists of thymol (50%), geranyl acetate, cymene, carvacrol and other volatile and aromatic compounds. Furthermore, the plant comprises a fatty oil, flavonoids, ascorbic acid and tannins (19%). Seeds have a large amount of fatty oils (28%).
Aerial parts contain: macro- and microelements: K, Ca, Mn, Fe, Mg, Co, Zn, Co, Mo, Al, V, Se, Ni, Sr, Pb.

Pharmacological properties. Oregano has sedative and mild hemostatic effect, stimulates the secretion of digestive glands, the motility of the gastrointestinal tract and biliary excretion, tones the smooth muscles of the uterus, has expectorant and airways sanitizing property, increases urination and increases lactation. It has a local anti-inflammatory, analgesic and antiseptic effect due to the present of thymol in the essential oil.

Application. Oregano has been used as a culinary and medicinal herb for thousands of years. It has a beneficial effect upon the digestive and respiratory systems and is also used to promote menstruation. It should not be used medicinally by pregnant women though it is perfectly safe in small amounts for culinary purposes. The leaves and flowering stems are strongly antiseptic, antispasmodic, carminative, cholagogue, diaphoretic, emmenagogue, expectorant, stimulant, stomachic and mildly tonic. The plant is taken internally in the treatment of colds, influenza, mild feverish illnesses, indigestion, stomach upsets and painful menstruation. It is strongly sedative and should not be taken in large doses, though mild teas have a soothing effect and aid restful sleep. Externally, oregano is used to treat bronchitis, asthma, arthritis and muscular pain. The plant can be used fresh or dried by harvesting the whole plant (but not the roots) in the late summer to dry and store for winter use.
Oregano is often used in the form of an essential oil that is distilled from the flowering plant. A few drops of the essential oil, put on cotton wool and placed in the hollow of an aching tooth, frequently relieves the pain of toothache. This plant is one of the best natural antiseptics because of its high thymol content. The essential oil is used in aromatherapy to treat the same kinds of complaints that the herb is used for.

Additional information:
You can find compiled information about oil of oregano research and studies here