Thebaine its name coming from the Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 Θῆβαι, Thēbai, an ancient city in Upper Egypt

Upper Egypt

Upper Egypt is the strip of land, on both sides of the Nile valley, that extends from the cataract boundaries of modern-day Aswan north to the area between El-Ayait and Zawyet Dahshur . The northern section of Upper Egypt, between El-Ayait and Sohag is sometimes known as Middle Egypt...

, is an opiate

Opiate

In medicine, the term opiate describes any of the narcotic opioid alkaloids found as natural products in the opium poppy plant.-Overview:Opiates are so named because they are constituents or derivatives of constituents found in opium, which is processed from the latex sap of the opium poppy,...

 alkaloid

Alkaloid

Alkaloids are a group of naturally occurring chemical compounds that contain mostly basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Also some synthetic compounds of similar structure are attributed to alkaloids...

. A minor constituent of opium

Opium

Opium is the dried latex obtained from the opium poppy . Opium contains up to 12% morphine, an alkaloid, which is frequently processed chemically to produce heroin for the illegal drug trade. The latex also includes codeine and non-narcotic alkaloids such as papaverine, thebaine and noscapine...

, thebaine is chemically similar to both morphine

Morphine

Morphine is a potent opiate analgesic medication and is considered to be the prototypical opioid. It was first isolated in 1804 by Friedrich Sertürner, first distributed by same in 1817, and first commercially sold by Merck in 1827, which at the time was a single small chemists' shop. It was more...

 and codeine

Codeine

Codeine or 3-methylmorphine is an opiate used for its analgesic, antitussive, and antidiarrheal properties...

, but has stimulatory rather than depressant effects, causing convulsions similar to strychnine

Strychnine

Strychnine is a highly toxic , colorless crystalline alkaloid used as a pesticide, particularly for killing small vertebrates such as birds and rodents. Strychnine causes muscular convulsions and eventually death through asphyxia or sheer exhaustion...

 poisoning at higher doses. However the "unnatural" enantiomer

Enantiomer

In chemistry, an enantiomer is one of two stereoisomers that are mirror images of each other that are non-superposable , much as one's left and right hands are the same except for opposite orientation. It can be clearly understood if you try to place your hands one over the other without...

 (+)-thebaine does show analgesic effects apparently mediated through opioid receptors, unlike the inactive natural enantiomer (-)-thebaine.