Dutch and Spanish scientists have warned that long-term use of the drug khat, obtained from a plant native to East Africa, lowers inhibitions with potentially dangerous results.
Reckless driving and criminal behaviour are some of the possible results of long-term use of khat, research leader Lorenza Colzato, a cognitive psychologist at the Netherlands' Leiden University, told AFP of the findings on Thursday.
"We can show that khat makes users more impulsive," she said of the leaf chewed to create feelings of mild euphoria, increased energy and enhanced self-esteem.
"It is associated with loss of self-control which may have dangerous consequences."
Colzato said the findings were significant because khat was the drug of choice of millions of people in Africa - about 60 percent of the population of Somalia and 80 percent of Yemeni's used it regularly.
Because of migration, khat was also used in "ethnic communities" worldwide.
"Yet nothing was known about whether it was dangerous or not", hence the two-month research project targeting long-term khat users of Somali, Yemeni and Ethiopian origin now residing in the Netherlands, where the drug is legal.
"This was the first research into the effects of long-term khat use on behaviour and cognitive functions" said Colzato of the findings by scientists from the universities of Leiden, Amsterdam and Granada, published in the scientific journal Frontiers in Cognition.
Test subjects were asked to press a button as soon as a green arrow appeared on a screen. If the colour of the arrow turned red, they were not supposed to press any button.
"In terms of accuracy and speed of response with the green arrows, khat users performed as well as non-users, but they found it much harder to restrain themselves when the arrow turned red," states the research paper.
New research will follow into khat's effects on memory and multi-tasking skills, said Colzato.