In A Nutshell
The people of Thailand have chewed the illegal kratom leaf for a cheap high for hundreds of years. The drug is thought to be no more dangerous than drinking coffee, but has been outlawed in Thailand for 70 years because the government worried that the chewing of kratom leaves would interfere with taxes derived from the sale of opium.
The Whole Bushel
Kratom is a tree in the coffee family found throughout Southeast Asia, particularly in Thailand. Its leaves are mildly psychoactive and have been chewed by Thai people for generations. The high produced by the leaves has been described as giving a coffee-like stimulation in low doses and a euphoric, sedative feeling in higher doses. Curiously, kratom is almost entirely used by men. (Thai women often chew on betel nuts, which are quite legal but contain known carcinogens.)
Although the potential long-term effects have not been widely studied, kratom seems generally harmless and is legal in most of the world, often pulverized and sold in pill form like herbal supplements. There is evidence that kratom can help those addicted to opiates such as heroin wean themselves off of drugs, much like methadone.
Despite the relatively innocuous nature of the plant, it has been illegal to grow or consume kratom in Thailand since 1943. The substance is grouped alongside marijuana and psychedelic mushrooms according to the 1979 Thai Narcotics Act. This is not out of any concern for the people, but rather because the government feared the consumption of kratom, which is cheap and grows naturally, would cut into the tax revenue they made from selling opium. The use or distribution of kratom generally involves a short prison sentence and a fine.
For decades, the law was not very intensely enforced, but in recent years a heavier crackdown has occurred as the Muslim youth of Thailand (who are forbidden from drinking alcohol by virtue of their religion) have begun using kratom to make a drink called 4×100. 4×100 is a cocktail made by boiling kratom leaves into a kind of tea, which is combined with ingredients like Coca Cola, cough syrup, and various other drugs including marijuana and sedatives. In rare cases, it has been reported that such bizarre additives as pesticides, paint, and the powder from inside fluorescent light bulbs has been used to increase the potency of the high.