Catha edulis is an evergreen shrub or tree of East Africa and the only member of its genus. Its fresh young leaves contain cathinone, an alkaloid with effects much like amphetamine, together with the weaker cathine. Cathinone breaks down within days of picking, and that one chemical fact explains most of how khat is grown, traded and used.
Names
The scientific name is Catha edulis (Vahl) Forssk. ex Endl. Catha is a Latin form of the Arabic name, and edulis means edible (PlantZAfrica). The plant has many common names. Khat and qat are the most widespread in English. It is gat in parts of Yemen, chat in Ethiopia, miraa in Kenya, and Bushman's tea in South Africa. The UK drugs advisory council also lists Abyssinian tea, tea of the Arabs and flower of paradise among its names (ACMD 2013, box 1).
One spelling trap: in UK slang "kat" or "m-cat" refers to mephedrone, a synthetic drug that has nothing to do with this plant. The ACMD noted that survey answers had confused the two.
Family and range
Catha edulis belongs to the Celastraceae, a family of trees, shrubs and climbers that in southern Africa alone counts about 60 tree species (PlantZAfrica). The genus Catha has a single, highly variable species (PROTA4U).
The plant is native to evergreen mountain forest in eastern Africa, from Eritrea south to the Eastern Cape of South Africa and Eswatini. PROTA places its likely centre of origin in the south-western highlands of Ethiopia. Arabic chroniclers of the 14th century already described khat growing in the mountains of Yemen and near Harar. It may have reached Yemen from Ethiopia as early as the 6th century, some 600 years before coffee, but Europe only learned of it at the end of the 18th century.
How to recognise it
| Part | Description (PROTA4U, PlantZAfrica) |
|---|---|
| Habit | Tree up to 25 m in forest; in cultivation a multi-stemmed shrub of about 2.5 to 6 m |
| Bark | Pale grey-green and smooth on young plants, rough and darker on old trees |
| Young twigs | Flattened, green to reddish brown; young stems pinkish |
| Leaves | 5.5 to 11 cm long, 1.5 to 4.5 cm wide, leathery, glossy, finely toothed edge |
| Leaf arrangement | Alternate on upright shoots, opposite on side branches |
| Flowers | 2 to 4 mm, five white or pale yellow petals, in small clusters in the leaf axils |
| Fruit | Hanging, three-sided capsule of 6 to 12 mm, red to brown, usually one to three seeds |
The leaves hang on short reddish stalks, which lets them twist in the wind. Young shoot tips and new leaves are reddish and turn green as they mature, which is why growers can name local forms by colour. More detail on the fruit and seed is on khat seeds up close.
Cathinone and cathine
The leaves contain alkaloids of the phenylalkylamine type. PROTA gives the total as 0.1 to 0.8 percent of dry weight, concentrated in the young leaves. Two of them matter most:
- Cathinone, chemically (S)-2-amino-1-phenylpropan-1-one. It was identified in khat in the 1970s, and pharmacologist Peter Kalix summarised the evidence in 1992 under the title "Cathinone, a natural amphetamine": in animal and human studies it acts like amphetamine, by releasing the messenger substances dopamine and noradrenaline from nerve endings (Kalix 1992).
- Cathine, also called norpseudoephedrine. It is formed from cathinone and is about ten times less potent (PROTA4U).
The leaves also contain a group of larger alkaloids, the cathedulines, which do not add much to the stimulating effect, and astringent tannins.
How much is in a leaf
Measured amounts vary widely. The ACMD report cites 78 to 343 mg of cathinone per 100 g of fresh khat. A Swiss study of market samples from Ethiopia, Kenya, North Yemen and Madagascar found that cathinone content tracked the price and the quality judgement of traders and chewers (Geisshüsler & Brenneisen 1987). In other words, the market's sense of good khat is largely a sense of fresh, cathinone-rich khat.
Chewing extracts most of it. In a study cited by the ACMD, four volunteers chewed an average of 44 g of khat for an hour and released about 90 percent of the cathinone. Blood levels peaked roughly two hours after chewing began.
Why freshness rules everything
Cathinone in harvested leaves is unstable. As cut khat dries, most of the cathinone turns into cathine within about 48 hours, and the ACMD gives fresh khat a usable life of 36 to 48 hours from picking. That is why bundles travel in plastic bags to keep them moist and why the trade runs on daily flights.
There is a nuance. A study from a United States Drug Enforcement Administration laboratory found that quickly dried khat keeps measurable cathinone for years (Chappell & Lee 2010). The loss happens mostly in leaves that wilt slowly, which is the normal fate of fresh khat on its way to market.
Risks recorded in the research
The same research that describes khat's chemistry also records its downsides. The ACMD lists raised blood pressure, heart rate and body temperature as acute effects, describes cases of serious liver damage in UK chewers, some of whom needed a liver transplant, and notes a generally mild form of dependence in some heavy users. These are reasons the plant is controlled in many countries; see khat and the law.