Betel
The Betel (Piper betle) is a spice whose leaves have medicinal properties. The plant is evergreen and perennial, with glossy heart-shaped leaves and white catkins, and grows to a height of about 1 metre. The Betel plant originated in Malaysia and now grows in India,  Indonesia and Sri Lanka. The best Betel leaf is the "Magahi" variety (literally from the Magadha region) grown near Patna in Bihar, India. The plant is known by a series of different names in the regions in which it is consumed - among these are Vetrilai (Tamil), Vettila (Malayalam).

# Ingredients
The active ingredients of betel oil, which is obtained from the leaves, are primarily a class of allylbenzene compounds. Though particular emphasis has been placed on chavibetol (betel-phenol; 3-hydroxy-4-methoxyallylbenzene), it also contains chavicol (p-allyl-phenol; 4-allyl-phenol), estragole (p-allyl-anisole; 4-methoxy-allylbenzene), eugenol (allylguaiacol; 4-hydroxy-3-methoxy-allylbenzene; 2-methoxy-4-allyl-phenol), methyl eugenol (eugenol methyl ether; 3,4-dimethoxy-allylbenzene), and hydroxycatechol (2,4-dihydroxy-allylbenzene).
Several terpenes and terpenoids are present in the betel oil as well.  There are two monoterpenes, p-cymene and terpinene, and two monoterpenoids, eucalyptol and carvacrol. Additionally, there are two sesquiterpenes, cadinene and caryophyllene.

# Chewing
In India and parts of Southeast Asia, the leaves are chewed together with the mineral slaked lime (calcium hydroxide) and the areca nut which, by association, is sometimes inaccurately called the "betel nut".  The lime acts to keep the active ingredient in its freebase or alkaline form, thus enabling it to enter the bloodstream via sublingual absorption. The areca nut contains the alkaloid arecoline, which promotes salivation (the saliva is stained red), and is itself a stimulant. This combination, known as a "betel quid", has been used for several thousand years. Tobacco is sometimes added.
Betel leaves are used as a stimulant, an antiseptic and a breath-freshener Paan. In Ayurvedic medicine, they are used as an aphrodisiac. In Malaysia they are used to treat headaches, arthritis and joint pain. In Thailand, Indonesia and China they are used to relieve toothache. In Indonesia they are drunk as an infusion and used as an antibiotic. They are also used in an infusion to cure indigestion, as a topical cure for constipation, as a decongestant and as an aid to lactation.
In India, betel is used to cast out (cure) worms.
In India, the betel and areca play an important role in Indian culture especially among Hindus. All the traditional ceremonies governing the lives of Hindus use betel and areca. For example to pay money to the priest, they keep money in the betel leaves and place it beside the priest.
The betel and areca also play an important role in Vietnamese culture.  In Vietnamese there is a saying that "the betel begins the conversation", referring to the practice of people chewing betel in formal occasions or "to break the ice" in awkward situational conversations.  The betel leaves and areca nuts are used ceremonially in traditional Vietnamese weddings.  Based on a folk tale about the origins of these plants, the groom traditionally offer the bride's parents betel leaves and areca nuts (among other things) in exchange for the bride. The betel and areca are such important symbols of love and marriage such that in Vietnamese the phrase "matters of betel and areca" (chuyen trau cau) is synonymous with marriage.
A related plant P. sarmentosum, which is used in cooking, is sometimes called "wild betel leaf".
WARNING: Chewing Betel has been associated with oral and esophageal squamous cell carcinoma.

# Further reading
- P. Guha: Betel leaf:The neglected green gold of India. J. Hum Ecol., 19(2) 2006 
- U J Nair et al: Role of lime in the generation of reactive oxygen species from betel-quid ingredients.